material CFM results and how CFM and MVTR relate to breathability

I currently have a hold of a very expensive anemometer so I decided I'd do some air permeability testing from some of the stuff I have, none of the garments are new and they have had various levels of wear but I did my best to find areas without wear. Testing was done with a vacuum cleaner, as such it may not respond linearly to resistance to airflow, high suction also causes the samples to deform under suction, this will increase the CFM compared to EN standard testing as when stretched the samples weave will open up.

Arc'teryx
Tyno(squamish): 35.31
Burly: 38.15
Fortius: 54.77

BD
Schoeller(alpine start): 34.15

Mountain Equipment
Helium AP(Kinesis): 27.97

Pertex
Quantum(double layer): 0 - The machine didn't like it.

So with this, I'd like to make a brief informative post regarding what CFM and MVTR are, how they relate to breathability and why you might care. The scope of this will mainly focus on wind jackets and soft shells as waterproofs are in general, much simpler.

CFM

CFM(cubic feet per minute) is a commonly used measurement unit for measuring volume flow in ducting and apparel, in apparel it is used to determine the air permeability of a fabric, basically, the fabric's wind resistance. The higher the number the more air permeable and less wind resistant the material is.

MVTR or WVTR

Moisture(water) vapour transmission rate, is the measurement that determines the rate at which moisture vapour can pass through a fabric according to specific test parameters in a lab, there are a few ways to perform this test but the most common is the upright cup method. This is the very high number you will see used for waterproof breathable fabric. Unfortunately, results from these tests are quite variable, they can be heavily affected by lab conditions and general airflow (is it a busy lab, is it in a cabinet, etc) as such these tests are only useful internally so don't bother trying to compare these results across brands. 

How do these relate to breathability?

Simply put, high CFM is a good indicator of breathability in warm environments, MVTR is a better indicator in cooler environments. This may be explained fairly simply by the simple fact that in a warm environment, the concentration gradient isn't there to get rapid diffusion through the fabric (you have no idea how few papers out there cover this). Anyone out there could go and rent or buy and return an expensive calibrated anemometer and test air perm reasonably accurately with just a vacuum cleaner but how is the general consumer supposed to determine MVTR? When using uncoated textiles like those found in a wind jacket or soft shell, the MVTR will be strongly correlated with its GSM, so in colder conditions aim for thin fabrics such as Pertex (not the air or quantum pro) as it will perform better and give better performance the colder it is. 

(though I would encourage everyone to email black diamond, Arc'teryx, Patagonia, Outdoor Research and all these brands to publish MVTR data, it will be far more helpful to 90% of us)

What does this mean for me?

Pertex air for the summer, Quantum for the winter. it's honestly that simple, lighter fabrics are quite a bit more breathable as a general rule and a high CFM wind jacket(such as a Patagonia airshed) should be avoided if you plan on being out in extreme conditions where you might want it to block the wind. 

 I've had a chance to do a real deep academic dive into all this stuff for my dissertation so if anyone has any questions, go for it. Merino vs polyester, material dry times, soft shell theory, anything.

I have always wondered how much garment color matters.  Is there research on this?  Is the coolest color white?

Here in the high desert(Red Rock Las Vegas) I feel like the Sun's impact is huge.  Last winter I was hiking and climbing in a black Kinesis Jacket but there were so many times I went from comfortable in the shade to baking in the sun.  I managed to swap out the black jacket for a yellow one this winter and have found it much better(I don't immediately bake if the sun peaks out from the clouds).

Mike K wrote:

I have always wondered how much garment color matters.  Is there research on this?  Is the coolest color white?

Honestly I think this a more physics question regarding light and albedo, I think white then red, yellow and orange are the colours that absorb the least energy from visible light.

I have however read some research on fibre profile and certain material adatives and it's increasing infrared emmitence which apparently has improvements on muscle temp, fatigue, and muscle recovery, so it might be worth looking out for baselayers with that function in the future.

Seeing there's nothing on the market like that, there is some stuff with ceramic fill which reflects infrared radiation which may help in addition to choosing a lighter colour. 

There's also physical alterations like calendering so shinier fabrics will reflect slightly more heat than non calander but minimal difference. 

that guy named seb wrote:

Simply put, high CFM is a good indicator of breathability in warm environments, MVTR is a better indicator in cooler environments. 

I don't think we can make this generalization.  These metrics are measuring two different things, and depending on the type of fabric one or the other may be more indicitive.  For example, for high CFM fabrics (ie highly breathable) move moisture by moving the air holding the moisture, whereas waterproof "breathable" (low CFM) fabrics must move moisture though other means (indicated by MVTR).  You'd need a lot more information about both the CFM and MVTR of the fabric, along with use case information, to make a claim about which is going to move more moisture.  Activity level, wind, humidity, etc.

This may be explained fairly simply by the simple fact that in a warm environment, the concentration gradient isn't there to get rapid diffusion through the fabric 

"Concentration gradient" of what, between where and where?

Kyle Tarry wrote:

I don't think we can make this generalization.  These metrics are measuring two different things, and depending on the type of fabric one or the other may be more indicitive.  For example, for high CFM fabrics (ie highly breathable) move moisture by moving the air holding the moisture, whereas waterproof "breathable" (low CFM) fabrics must move moisture though other means (indicated by MVTR). 

MVTR and CFM are inherently linked but a high CFM doesn't strictly mean higher MVTR, factors such as fabric thickness, fibre composition and fibre coating such silicone encapsulation will have have a negative effect on the rate at which water vapour can transmit through the fabric even if it let's air through relatively easily. 

Both CFM and MVTR can be considered a measurement of breathability, the reputation of "breathability" of waterproof breathable membranes is well deserved but the failings of WPBM is not because MVTR is a poor indicator. It's because WPBM's a quick to wet out, soil, and get overwhelmed though this can be improved through incorporating hygroscopic materials such as wool into your layering system. 

 You'd need a lot more information about both the CFM and MVTR of the fabric, along with use case information, to make a claim about which is going to move more moisture.  Activity level, wind, humidity, etc.

Movement of moisture within garments is very multi factored and I don't want to bore people to death by talking about air movement through multi layered permiable fabrics, air pump effects through movement or speculate on this poorly researched area. 

The studies I am referring to that have tested user comfort and CFM vs MVTR were looking at full body PPE and came to opposing conclusions as to which was the greatest predictor of comfort MVTR or CFM, the conditions and exertion were similar in both tests asside from different temperatures and humidity. So with these findings, I'd be happy to say as a general rule MVTR is important when cold, high CFM is preferable when warm. 

High humidity environments will always be much less comfortable and there is no research done on this topic that I could find that would be relevant to climbers, conditions like being stuck in a cloud haven't been looked at, I can tell you virtually every material would suffer as there has been studies looking at MVTR with fabrics when wet using guarded sweating Hotplate and it has a significant negative effect on mvtr. In these conditions a high CFM may help comfort slightly but I would say drying out after being soaked inside out by clouds would be the priority, my own testing has shown MVTR and fabric thickness are the largest factors that effect dry time. 

"Concentration gradient" of what, between where and where?

Heat and water vapour are the primary factors to consider when talking about moving moisture and maintaining comfort from a thermophysological standpoint, having an exaggerated difference between the humidity and temperature between the inside and outside of garments will leader tk the fabric being more breathable. Higher mvtr allows your bodies own thermoregulation to work by sweating and evaporating while also maintaining a microclimate within your garments that isn't too hot and humid. 

If you're doing a dissertation on fabric performance, I recommend getting in touch with your local military folks. They spend lots of time and money on figuring out how well clothing performs. They also have the good testing rigs, which will save you mega time not reinventing. And they may have more broadly pressing questions than what parka climbers should wear.

dave custer wrote:

If you're doing a dissertation on fabric performance, I recommend getting in touch with your local military folks. They spend lots of time and money on figuring out how well clothing performs. They also have the good testing rigs, which will save you mega time not reinventing. And they may have more broadly pressing questions than what parka climbers should wear.

Natick do an excellent job with their research on military apparel and a surprising amount of the research is available to the public. They research everything from parachute materials to "what parka should soldiers wear". 

Their labs are incredible, thermal sweating mannequins are top tier bits of kit. 

I have referenced them extensively in my dissertation. 

that guy named seb wrote:

MVTR and CFM are inherently linked but a high CFM doesn't strictly mean higher MVTR, factors such as fabric thickness, fibre composition and fibre coating such silicone encapsulation will have have a negative effect on the rate at which water vapour can transmit through the fabric even if it let's air through relatively easily. 

I'd be very interested in test data that shows a high CFM fabric performing worse at removing moisture than a low CFM fabric, in an environment with significaint ambient air movement (e.g. wind, motion, and activity).  I believe the above quote could be true in a lab when doing the standard MVTR test (since it depends wholly on diffusion of moisture in still air), but that isn't representative of actual moisture management in the outdoors.

Note: the amount of moisture moved by airflow is WAY higher than the numbers moved by diffusion per the MVTR test.  For example, at 10 CFM (over the standard ATSM D737 38 cm2 sample area) and 10g moisture per cubic meter of air (100% humidity at 10C or ~30% humidity at body temp), you move ~1,000,000 g of water per 24 hr per m^2, compared to typical MVTR results of 10,000-30,000 g/m2/24h.  I.E. the movement of air is moving 100X as much moisture as diffusion.

The studies I am referring to that have tested user comfort and CFM vs MVTR were looking at full body PPE and came to opposing conclusions as to which was the greatest predictor of comfort MVTR or CFM, the conditions and exertion were similar in both tests asside from different temperatures and humidity. So with these findings, I'd be happy to say as a general rule MVTR is important when cold, high CFM is preferable when warm. 

Can you provide a link to these studies?  The details of the methodology and the results are important if we're going to interpret them to mean particular things for garmet selection for our usage.

High humidity environments will always be much less comfortable and there is no research done on this topic that I could find that would be relevant to climbers, conditions like being stuck in a cloud haven't been looked at... In these conditions a high CFM may help comfort slightly

It seems like this environment is the most relevant to climbers, as we get wet and wear shells primarily when the environment is humid?

my own testing has shown MVTR and fabric thickness are the largest factors that effect dry time. 

Can you post your test methodology and data?

Heat and water vapour are the primary factors to consider when talking about moving moisture and maintaining comfort from a thermophysological standpoint, having an exaggerated difference between the humidity and temperature between the inside and outside of garments will leader tk the fabric being more breathable. 

Sure.  But you specifically said "in a warm environment, the concentration gradient isn't there to get rapid diffusion through the fabric".  That's not really accurate, is it?  You can have a warm environment that is low humidity; in fact since warmer air can hold more moisture it's preferrable for accelerating evaporation (it's no coincidence that a clothes dryer uses heat).

Higher mvtr allows your bodies own thermoregulation to work by sweating and evaporating while also maintaining a microclimate within your garments that isn't too hot and humid. 

Air movement also allows the body's thermoregulation process to work, think about the chill you get if you're sweaty on a windy day.  That's why wind makes us cold when we're sweaty and why we use fans to cool us off in warm climates.

Kyle Tarry wrote:

I'd be very interested in test data that shows a high CFM fabric performing worse at removing moisture than a low CFM fabric, in an environment with significaint ambient air movement (e.g. wind, motion, and activity).  I'm dubious of the result you claim.

I have yet to see any papers looking at the effect of wind on high CFM jackets and removing moisture from the jacket, no doubt it would be higher but what is the purpose of a wind jacket or soft shell if it's not windproof? Results are in my dis, read the end message.

Note: the amount of moisture moved by airflow is WAY higher than the numbers moved by diffusion per the MVTR test.  For example, at 10 CFM rating (over the standard ATSM D737 sample area) and 10g moisture per cubic meter of air (100% humidity at 10C or ~30% humidity at body temp), you move ~1,000,000 g of water per 24 hr per m^2, compared to typical MVTR results of 10,000-30,000 g/m2/24h.  E.G. the movement of air is moving 100X as much moisture as the diffusion through the member can.

As I said, CFM is a factor in breathability, it just becomes a worse predictor of wearer comfort in cooler conditions.

Can you provide a link to these studies?  The details of the methodology and the results are important if we're going to interpret them to mean particular things for garmet selection for our usage.

sure, http://dx.doi.org/10.1080/15459620500498133 and https://doi.org/10.1080/15459624.2013.875181

It seems like this environment is by far the most relevant to climbers, as we get wet and wear shells primarily when the environment is humid.

It will help as far as CFM is somewhat linked to MVTR so dry time will be improved but there is no getting away from being submerged in a cloud and being soaked through High CFM low CFM high MVTR low MVTR, you are soaked. Synthetic materials become pretty much entirely impermeable to moisture vapour once soaked, wool does better but still a massive drop. I could see having a high CFM outer moving water vapour out of a system with a lot of wind but then this would lead to quite the chilling effect, use of a garment like a nano air which will have air channels between the two high CFM layers would be the better option of avoiding getting very cold.

Can you post your test methodology and data?

The methodology was simple timed measurements of fabric weights to determine dry time, samples were placed on some 7mm spacer mesh with the face of the fabric facing up, no air flow. I decided on this as opposed to the standard hanging dry test as the hanging dry test isn't particularly relevant to the drying of clothing that someone is wearing. The samples tested were predominantly double weaves so this will have affected the importance of MVTR in dry time as they will have had a good amount of capillary capacity on the underside of the fabric.

This certainly isn't perfect and needs some development, one sample wicked heavily into the spacer mesh which initially made it seem like it was drying very quickly but then quickly slowed down and continued to dry in line with the expected rate. 

Sure.  But you specifically said "in a warm environment, the concentration gradient isn't there to get rapid diffusion through the fabric".  That's not really accurate, is it?  You can have a warm environment that is low humidity; in fact since warmer air can hold more moisture it's preferrable for accelerating evaporation (it's no coincidence that a clothes dryer uses heat).

If it's warm all you have is concentration diffusion if it's cold you also get thermal diffusion.

Air movement allows the body's thermoregulation process to work, think about the chill you get if you're sweaty on a windy day.

Air movement accelerates the evaporation of sweat disproportionally to the amount of cooling needed, hence the need for wind jackets. The human body does really well at regulating itself to not overheat without the need for wind. 

I'm currently awaiting feedback on my dissertation which contains the test results and write-up on the methodology. If you would like to DM me I can send you a spreadsheet with the data from the samples I tested.

that guy named seb wrote:

I have yet to see any papers looking at the effect of wind on high CFM jackets and removing moisture from the jacket, no doubt it would be higher but what is the purpose of a wind jacket or soft shell if it's not windproof? Results are in my dis, read the end message.

The purpose isn't to fully block the wind, the purpose is to reduce it to an "appropriate" level.  If we just wanted to fully block the wind, we would simply wear trash bags, silnylon, or dyneema wind jackets.  However, a light breeze provides the best comfort when doing high exertion, so a wind jacket that allows some air transfer is best.  The amount of "ideal" breathability is highly dependent on the circumstances, which is why the "right" garment is difficult to point a finger at, and why ventilation elements such as zippers are so valuable.

 http://dx.doi.org/10.1080/15459620500498133 and https://doi.org/10.1080/15459624.2013.875181

These are behind a paywall, so the data isn't available to view.  However, note this quote from the first article:

     "Air permeability was a better predictor of fabric work limiting performance than MVTR"

This test has a reasonably good methodloogy, since they evaluated limits on human exertion with a whole system including different shell fabrics.  This seems like it would be a decent corrolary for us outdoor enthusiasts, so their conclusions with regard to breathability seem relevant.

It will help as far as CFM is somewhat linked to MVTR so dry time will be improved but there is no getting away from being submerged in a cloud and being soaked through High CFM low CFM high MVTR low MVTR, you are soaked. Synthetic materials become pretty much entirely impermeable to moisture vapour once soaked, wool does better but still a massive drop. I could see having a high CFM outer moving water vapour out of a system with a lot of wind but then this would lead to quite the chilling effect, use of a garment like a nano air which will have air channels between the two high CFM layers would be the better option of avoiding getting very cold.

I think this is getting off onto a tangent, so I'll let it drop.

The methodology was simple timed measurements of fabric weights to determine dry time, samples were placed on some 7mm spacer mesh with the face of the fabric facing up, no air flow. I decided on this as opposed to the standard hanging dry test as the hanging dry test isn't particularly relevant to the drying of clothing that someone is wearing. The samples tested were predominantly double weaves so this will have affected the importance of MVTR in dry time as they will have had a good amount of capillary capacity on the underside of the fabric.

Are your conclusions on CFM vs MVTR based on this test data?  I think there might be a gap here.  CFM breathability is a measure of the air permability of a fabric when it is subjected to a pressure differential (e.g. wind).  If you did a drying time test without air flow, you've effectively removed that variable from the fabrics.  I would not expect the air permability to be a significant factor, if the test is conducted in an environment without air movement...

For a fabric user, the time the outer shell takes to dry when laid in a static ambient condition isn't a good metric.  Wool would do very poorly in this test, yet we know wool is very effective.  The purpose of a shell fabric isn't simply to dry fast in a lab when it gets wet.  The goal is to create a comfortable microclimate for the user, keeping the core temperature in an appropriate range and managing moisture.  A thin piece of plastic will "dry fast" if you sit out it in a lab, but that doesn't make it a good choice for managing the microclimate for an active, sweating individual in the outdoors.  We're trying to move moisture off an inner layer (skin, baselayers), while recreating (moving) in an outdoor environment (probably some wind).  That's a very different test scenario...

If it's warm all you have is concentration diffusion if it's cold you also get thermal diffusion.

You initially said "in a warm environment, the concentration gradient isn't there."  Sorry, I am confused by this.

Air movement accelerates the evaporation of sweat disproportionally to the amount of cooling needed, hence the need for wind jackets. 

Right, this is exactly why fabrics with some air permability are so beneficial for managing temperaure and moisture, because this effect is so pronounced.

The human body does really well at regulating itself to not overheat without the need for wind. 

We know the joy of a breeze when they are hot and sweaty walking uphill.  Assisting with the cooling process is helpdul, especially if we don't want to sweat heavily (to preserve water, keep layers dry, etc.).

I'm currently awaiting feedback on my dissertation which contains the test results and write-up on the methodology. If you would like to DM me I can send you a spreadsheet with the data from the samples I tested.

I think we might be better served by waiting until the data can be made public before drawing further conclusions from it.

Are you by chance Steven Seeber, that did a big article on Backpacking Light about this? Most of it is behind a pay wall, but lots of info in the discussion pages:

https://backpackinglight.com/forums/topic/by-the-numbers-fabric-air-permeability-and-mvtr-are-closely-related-just-not-how-you-might-expect/

Telefly wrote:

Are you by chance Steven Seeber, that did a big article on Backpacking Light about this?

Haha, no I'm just a student, Steven has a consulting company that specialises in turning test data into marketing material and communicate it with customers in the form of marketing. 

He did a test (sadly behind a pay wall) he found the higher mvtr goretex shakedry to outperform wind proofs in cold conditions. He measured this by seeing how much sweat was absorbed by his baselayer, weighing it before and after the tests. 

Kyle, you might want to reread some of what I wrote. I'd love to explain in depth every concept I talk about here but even my 12,000 word dissertation wasn't able to properly expand on everything I've talked about. I encourage you to wait for my dissertation and then do the reading, if you can't access anything in there, sci-hub.se is a great tool though you may need a vpn to access it. 

Sorry Seb, I've been out recreating for the last week and kinda lost track of this.

that guy named seb wrote:

Kyle, you might want to reread some of what I wrote.

I've looked over it a few times, and nothing new is jumping out at me.  Is there something specific you're thinking of?

A few thoughts, which I have attempted to be less verbose about:

• I do not think that drying time of saturated fabric in still air is a good test of fabric performance during usage.
• The test by Gonzalez et al that you reference ( tandfonline.com/doi/abs/10.…) appears to contradict your claims.  A few short excerpts from this report:
  • "MVTR did not predict average sustainable metabolic rate or total evaporative resistance for the ensembles in this study" (p85)
  • "Air permeability rates were better correlated with ensemble performance than MVTR. Higher air permeability rates were associated with higher critical speeds (see Figure 4) and metabolic rates. An improved relationship between air permeability and Re-t was also found" (p85)
• Anecdotal evidence suggests that air permability is an important element to maintaining comfort while active.  There are lots of reviews, advice from expert climbers, etc. that support this.  I acknowledge that this isn't very scientific, but it still bears consideration.

Beyond this, I don't think that I have much more to say, especially in lieu of your experimental data.  I think it's awesome that you're testing this stuff in a scientific way, but I am not convinced that we should overturn the currently accepted principle that air permeable materials work best for managing perspiration and temperature while doing high output activities.

Kyle Tarry wrote:

Sorry Seb, I've been out recreating for the last week and kinda lost track of this.

I've looked over it a few times, and nothing new is jumping out at me.  Is there something specific you're thinking of?

A few thoughts, which I have attempted to be less verbose about:

• I do not think that drying time of saturated fabric in still air is a good test of fabric performance during usage.

If by performance you mean realistic interpretation of dry time I would somewhat agree, it doesn't give an accurate indication of dry time, what it does do however is give a solid indication within the scope of the research I was conducting of how the fabrics dry relative to one another. In this case we were looking at wool samples vs a selection of synthetic fabrics provided by a few well known brands. 

• The test by Gonzalez et al that you reference ( tandfonline.com/doi/abs/10.…) appears to contradict your claims.  A few short excerpts from this report:
  • "MVTR did not predict average sustainable metabolic rate or total evaporative resistance for the ensembles in this study" (p85)
  • "Air permeability rates were better correlated with ensemble performance than MVTR. Higher air permeability rates were associated with higher critical speeds (see Figure 4) and metabolic rates. An improved relationship between air permeability and Re-t was also found" (p85)

Yes this was the study that indicates a high CFM is a better indicator of comfort, it was done in a very humid and warm test setting. The other study indicates the opposite with the biggest difference being the temperature and humidity. 

• Anecdotal evidence suggests that air permability is an important element to maintaining comfort while active.  There are lots of reviews, advice from expert climbers, etc. that support this.  I acknowledge that this isn't very scientific, but it still bears consideration.

I thinking this may be where you are misinterpreting what I'm saying, I am talking about general indicators, never have I said maintaining a level of air permeability is unnecessary or non beneficial, even goretex which was always air immpermiable is now air permiable with "goretex pro most breathable". 

I have also read of numerous people speaking of super high CFM shirts like the patagonia airshed, that it's not wind resistant enough and they would just wear a Sunhoody instead as if the weather and levels of exertion were to call for such a high CFM jacket they might as well wear something with considerably higher air permiability. Even jackets like the squamish and bd have also been described as not windproof enough. 

Beyond this, I don't think that I have much more to say, especially in lieu of your experimental data.  I think it's awesome that you're testing this stuff in a scientific way, but I am not convinced that we should overturn the currently accepted principle that air permeable materials work best for managing perspiration and temperature while doing high output activities.

I'm not trying to overturn everything, I am simply expanding on what has been known for years. Goretex(high mvtr) works best when it's cold and dry!

that guy named seb wrote:

If by performance you mean realistic interpretation of dry time

I mean functional performance of the garment during use, where its job is to maintain an appropriate micro climate for the user.

Yes this was the study that indicates a high CFM is a better indicator of comfort, it was done in a very humid and warm test setting. The other study indicates the opposite with the biggest difference being the temperature and humidity. 

The other study (Chen 2016) does not indicate the opposite.  The "A" and "B" test garments, which have slightly different air permeability/MVTR ratings, are virtually indistinguishable in the results.  The only meaningful conclusion is that the A and B outfits were better than "C", which had less air permeability and MVTR.  There is no datapoint that I see that indicates that MVTR is a larger driver of performance than CFM.

"It appears that the difference between air permeability and water vapor permeability (including moisture transfer and heat transfer) is not obvious."

Is there a section of results for that paper which I missed?