Down and Compression

I am not an expert, but everything that I have read says that it is fine to compress it daily, but essential to allow it to loft up at night. Long periods of uninterrupted compression will reduce its ability to loft back up.

Sounds like a good subject for an experiment in the BPL labs.

There are a lot of opinions on this subject, but most of the "evidence" seems anecdotal. How about some of the science that BPL has been putting into stove CO emmissions?

Joshua, I have bought three down bags, all 725 fill power, and they all came to me tightly compressed in their stuff sacks; presumably for months. The bag I got on clearance had been tightly compressed for at least 2 years. They all fluffed up very well (i.e. more loft than required for the indicated temperature rating). I store them in big pillow cases, and stuff them as small as I can when packing. My Montbell #7Alpine compresses down to a ball the diameter of a CD. I take no special precautions other than to keep them dry.

my understanding is that it is the COMPRESSION CYCLES that cause the problem. how so? like with so many things FRICTION and FATIGUE are the problems. the repeated rubbing of the insulation and possbily sharp curvature of some the fibers during compression and expansion causes the insulation to break down over time/cycles.

this can happen in a sleeping bag which is virtually never compressed or even stuffed, but rather is merely used prit near daily by sitting and laying on it.

This could occur, for example, like with a sleeping bag used on an old recliner in someone's den (who might that be, i wonder, hmm…) that after years has flattened considerably.

i don't think the periodic laundering is to blame as only the bottom insulation of the sleeping bag is affected, not the other parts of it. The bottom is both sat and layed on, while the entire bag is periodically laundered.

Sitting, rising, moving about on the bag has caused the bottom insulation to breakdown – either from friction, fatigue, or both. This one is an old MtnHW synth. bag filled with Polarguard 3D.

Supposedly, down is more resiliant than any synth and it can tolerate more compression-expansion cycles w/o breaking down (yes, another pun – my vocabulary is rather limited).

How much can down be compressed?
How do you tell when you have compressed it too much?

Doug

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Douglas,

the rule of thumb is to NOT compress it

a) in a compression sack

b) in a NON-compression sack smaller than that supplied by the manufacturer (i don't mean here the larger cotton or mesh storage back, but rather the smaller stuff sack generally included).

if the manufacturer supplies a compression stuff sack, my advice, which you should reject when more knowledgeable advice posts back, is to NOT use the compression feature of that sack (or use it minimally if you feel that you really must) – just stuff the bag into it without using the compression straps.

I still wonder why in the (ultra) leightweight comunity there is so much fear of and emphasis on the compression of a down sleeping bag.

A down sleepingbag will last you a decade or two with normal use and an occasional washing session. Normal use here is when the SB is used a couple of weekends per year and on a two week holiday and maybe some additional use in a holiday season.

(Utra)leightweight backpackers are gear heads. If you now own a 16 oz SB and next year a 12 oz SB that will give you the same performance will hit the market you'll start saving money and buy the leighter SB. But the 16 oz SB is still very serviceable. It'll still keep you warm on nights within it's intended use spectrum, but we're no longer in love with this poor SB cause it's 4 oz too heavy. We have a new love affair with the 12 oz SB.

Maybe you've used this poor old SB for two years, maybe four, but it would service you for at least another decade.

So can anyone pleeeaaase explain to me why you shouldn't overstuff the heck out of your SB in the few years you think it wothy of being in the backpack you currently use (untill that also has to spend the rest of it's day in the 'too heavy' closet, reminising with it's old palls how great it was when you still treated them with respect, loved them and took them out to see the mountains, desserts and sea sides.)

:'(

So my advise IS and will remain: just put your SB in the smallest, tightest compresion sack you can put it into if you need the space.

Eins

I must say that seems very true. good point

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Eins,

Hear ya'. Understood. I was too theoretical in my post and totally ignored the practical aspects which you astutely pointed out. You make a good PRACTICAL point. I've parted with quite a bit of gear that showed (and often had) very little use, or nights/miles on it, and much, much life left in it.

If we don't expect to be keeping our down SB for 10yrs, but only for, let's say 4yrs (assuming these numbers also are actually representative of both maximum life with little or no compression, and service life with extreme compression), then why not compress?

For me as an OCD engineer, it's more of the "just in case…" aspect – so i don't compress. But, i'd have to admit that the "just in case…" has never happened to me. Yet!!

Hmmm…gives me something to consider (or re-consider)…

I definitely hear the practicality aspect as well. Good point.
But when one shells out hundreds of bucks for Nunatak or BMW gear, many people (or maybe just me) no doubt sign a mental agreement that it's the last sleeping bag I will buy for a LONG LONG time. It's the best way to rationalize the gear addiction. Besides, my grandaddy taught me to respect and take care of my tools, that extends to sleeping bags as well.

A number of people on this site whose input I tend to respect have commented in past threads that they put their SB in an oversize sack along with other compressable items.
Then they put this sack in the bottom of their pack and let the heavier items above do the compressing/stuffing. The implication is: the less compression, the better. That is intuitive to me and is a procedure I have followed for many years. Possible supporting evidence: every Western Mountaineering SB I have ordered(5 to date) has come in an oversize box loosely rolled. It does seem to me that, as you compress a SB smaller and smaller, there will come a point where a certain percentage of feathers will be bent along their spine to angles approaching 180 degrees. Over time, it seems to me, this would affect their lofting ability. Just intuition/speculation. May upbringing, too, because, like Johsua, my Dad taught me to take care of my tools. I'd be interested in feedback.

Joshua and Tom,

Over compressing your SB will leed to a shorter live of your SB. I have a G4 and that has a wider bottom so you can store your SB loftly. I do so cause I need that loft to raise my CG.

My point is that most UL-ers disregard their SB long before there is any significant demise in loft. So I see no point that IF you need to pack your SB as tiny as possible (cause you need to have the space in your tiny backpack) to refrain from doing so. And I see no point in worrying about loosing loft in your SB when you know that you'll disregard itlong before the end of it's days.

Maybe when thru hiking for an entire season….

A short lesson in down.

There are feathers and there are down. Feathers have a shaft from witch tiny hairs stick out* more or less in one plain. By bending one of those to 180 degrees the shaft will break.

Hopefully you've down in your SB. Down has a center from which the hairs stick out in all directions. Down keeps you warm, feathers add weight while doing nothing. Hence the 80/20; 90/10; 95/5 indications on many SB's to show you how much useless feathers compared to down there are in your SB.

Eins

*sorry for my poor choice in words; couldn't think of a nice English word.