Is compressing down bad a myth?

Thought I'd find a lot via search but not really.  I typically shove my sleeping bag into the bottom of my pack but I need to cram my WM Alpinlite 20F into a 40L pack w/ other winter gear.  Is really full compression (for a day) really as bad for down as I've been told?  I think it's 800 FP but I'm not sure (manuf website doesn't say; mines from 2016)

I normally have my 0 degree down bag compressed really small when it's being used on trips and then I store it uncompressed. I made the mistake of storing it compressed for a few months and noticed a pretty big loss in warmth, but haven't noticed any changes from having it compressed for a day or 2. 

I find that using a slightly bigger stuff sack is much better than cranking down a compression sack for a few reasons. For one, your pack carries much better when the dead space is filled. It's very hard to pack our the dead space when your sleeping bag is a tight little ball. While down is great at rebounding from being *lightly* compressed, cranking down the compression straps is definitely not good for the longevity of the bag. This also makes it take much longer to re-loft when you get to camp.

Arthur W wrote:I typically shove my sleeping bag into the bottom of my pack but I need to cram my WM Alpinlite 20F into a 40L pack w/ other winter gear.  

You would be surprised at how much less damaging this is that a over-cinched compression sack. This is totally within normal and fine use.

Probably not good.

Definitely not as bad as synthetic.

In the end, does it matter? There's no realistic alternative; nobody is going to climb with a huge pack just to give their down bag extra room to fluff. Stuff it and go climbing. If one day you find it's not warm enough anymore, buy a new one. It'll probably take years.

Ability to compress small is a major reason for buying a down bag, so do it when you need but for minimum time practical.

Never using your down bag, and keeping it loose on the large top shelf of your closet will ensure that it lasts a very long time! But I’m guessing you bought it for a reason other than occupying a shelf in the closet.

Compress it when you need to. Keep it loose when not in use. This is what the bag is meant to do, in the course of its useful life. 

Compression will not kill your bags. Just store hanging it in the giant sack they come with.

I have a few mid-higher end bags and jackets of various temp ratings that have lasted me years with a lot of backpacking/mountaineering  (during which they are fully compressed). I still feel they hold their temp rating.

You’ll probably lose more from not properly washing them. 

one of the advantages to high-quality down is its compressibility for packing.  truly high-quality down ("garment grade" defined as minimum 90% down plumules, and maximum 10% pin feather content) won't be damaged by tight compression - as long is its not left tightly compressed for long periods of time (stored for weeks or months tightly compressed).  on a trip, you're decompressing it to use ieach night, so its not left compressed for extended periods.   compression can be an issue with lower qualities of down (up to 20% pinfeather content) because the feather stems don't compress and spring back like down plumules.  the pinfeather stems break, resulting, over time, in loss of loft.  so whether you're damaging your down gear by tightly compressing it depends on the quality of down in your gear.  Most of your marquee brands using 800+fill down are achieving that fill volume by using the "garment grade" 90/10 down, but if you drop to 500 or 650 fill, you're likely buying the 80/20 grade, and it will not hold its loft as well over years of repeated tight compression.  either grade will last much better if always stored loose/unstuffed.

Compressing for a short time is no problem, just store it properly when not in use so that the loft comes back (so to speak).

...and none of this is myth worthy. Plenty of threads and articles address this at length.

my old mentor told me it's ok to compress as long as it is completely dry.  the wetter it is, the less you should be compressing.  kinda made sense so i never did anything else.