Compressing down: What’s the science?

actually its hard to believe, but not compressing can actually free up more space, heres why: When you compress into a stuff sack you form a decent sized ball. In the case of my JRB quilts, probably around the size of a cantelope. Imagine dropping a cantelope in the bottom of your trash compactor bag then putting stuff on top of it. alot of free space will be wasted right? When you store uncompressed you fill up those free spaces. I never make my stuff sacks super tight and rigid, better to be loose so it conforms to the empty spaces in the pack.

As far as compressing down, according to the science gods the whole of the law shall be: thou shall not compressith down quilts whilst stored.

Most quality bags come supplied with both a large cotton bag for storage and a small stuff sack for compressing when hiking.

While it's perfectly OK to compress your bag for a day or three when hiking — never store your bag long term in a compressed state. And when hiking, I like to first set up camp and lay out the sleeping bag to give it time to loft back.

EDIT: Reading Isaac's response above… I also don't use stuff sacks. Why? Because not using them means faster packing AND more efficient use of pack space. That said, using them on your hikes won't hurt the bag.

Same here, I just stuff my quilt in the bottom of my pack, and shove as much more stuff as I have on top of it. It automatically compresses to fill my pack, which is a good thing, but it's never heavily compressed.

Apart from the obvious relofting times people are aware of, I just want to point out that from what I've seen making quilts, if the down gets seriously compressed (which most of it does in shipping bulk from suppliers), I've seen it take a day or two to reach full loft.

I don't think the "damage" concern is all that real, atleast not from the standpoint of permanence, but it can definitely affect performance on the trail.

Compression does not hurt down in my experience. On my early long distance hikes – the Pacific Crest Trail in 1982 and Continental Divide Trail in 1985 – my down sleeping bag was squeezed into a small stuffsack. Those were 51/2 month long walks and the sleeping bags lofted as well at the finish as at the start. I stopped packing my bags like that many years ago because it's inefficient, as others have pointed out. I now pack my down bag in a large stuffsack which then fills out the bottom of the pack and is compressed by the gear on top of it.

Many years ago I also saw a down bag that had been vacuum packed for a year in a survival kit for the British Antarctic Survey. When unpacked it looked totally flat at first but soon lofted fully whe shaken out and allowed to warm up.

I don't store down bags in stuffsacks because if there's any humidity it could damage the down. Laying bags out flat or keeping them in big cotton or mesh storage bags ensures they can air and any dampness isn't trapped inside. You only need to smell one mildewed down bag to know you really want to store bags dry!

"Many years ago I also saw a down bag that had been vacuum packed for a year in a survival kit for the British Antarctic Survey. When unpacked it looked totally flat at first but soon lofted fully whe shaken out and allowed to warm up."

Chris — that's very reassuring to know. If a down bag can survive vacuum packing for a whole year, then no stuff sack can do it harm!!

The point Chris made here is crucial. Down can be compressed with little damage for a long time provided that it is really dry.

But in the field the average bag is not really all that dry, so compression for a long time is not good. Just overnight – the down can handle that if it has to.

At home the bag should be stored fully uncompressed, to help the down expand and dry. Both are important to long life.

Note that down is very different from synthetics here. Compress any of the synthetics hard and they suffer, immediately. Very different stuff.

Cheers

Yes, we all know to store our bags at home all lofted up, and to keep them dry.

My question is the practical one about what to do in the field, and I'd guess a lot of BPL'ers want to know this as well:

If I'm hiking from 7 a.m. to 5 p.m., is it okay to stuff my down sleeping bag into a little, teeny compression stuff sack (with straps) for the duration? And it'll fluff out just fine at 5 p.m., and suffer no medium- or long-term damage to the loft? (Who here is or is not willing to risk this?)

Or do I need to award it a little more space than that in my pack?

Does the answer change if conditions are wet/humid/rainy?

Thank you.

Elizabeth, I do that all the time.

Just make sure that you air the bag out in the morning to minimize any moisture. When you get into camp at the end of the day, pull out the bag and shake it loose for a few minutes. Maybe hang it in the sun for a few minutes, assuming that the air is dry. Then shake it again every half hour until time for bed.

If it is a quality down bag, I would not expect it to be damaged by compressed carrying.

–B.G.–

Not all down is equal. Down is a blend between the fluffy down clusters and feathers.

The fluffy down custers are composed of very fine substructures or microstructure. You can't compress a poluyester microscope slide, nor a glass microscope slide — because they break. You can compress a mass of polyester fibers or a mass of fiberglass fibers can be readily compressed. This is a reflection of thinness. If you have had the class in "Strength of Materials", thinness in materials promotes easy compression (actually, bending and/or torsion and/or buckling) of a mass. For example, a steel fiber mass, such as a scouring pad, compresses easily, but a solid one piece steel bar doesn't.

Feathers are composed of microstructural elements that are generally thicker than the microstructural elements of a down cluster. Not only are masses of feathers harder to compress because of this geometric factor, the microstructural elements of feathers, particularly the thicker and stiffer stems, will break upon compression.

It is the very microstructural fineness of down microstructure that is a basic building block for compression without damaage.

There are other factors in addition to the fineness. Humidity is often a plasticizer for organic structures. Heated steam, for example, will let you permanently bend wood into fine furniture or sculptural or tool items. Without the plasticizer effects of steam and heat, you can't generally do that with wood creative permanent bendings of large amount.

So there is a physical basis to the cautions of humidity and compression for a long time. You would expect that under humid conditions, the down clusters when highly compressed could more or less permanently assume a less fluffy configuration related to the plazticizing activity of humidity (water vapor or cold steam).

This humidity effect is postulated to be possible on general principles known to apply to other organic materials. I have no direct experience of humidity effects on the long term compression of down.

There was a masters dissertation on the mechanics of down written at the Georgia Institute of Technology within the last 5 years. It focused on the elastic compression characteristics and models for use in analysis of down deformation.

This reminds me of the old debate as to whether it's better to stuff your down or roll it. Some think that stuffing down causes more shearing forces than rolling, other think rolling is bad (can't remember why). I do both depending on the situation. Most of the time I just stuff my down into the bottom of a large dry sack, then put the rest of my *must stay dry* stuff on top. It usually turns out the bag is lightly to moderately compressed when I do this. But lately I have been rilling my cuben quilt into a very compact roll, and haven't (yet) noticed any effect on the loft.

Hi Elizabeth,

I never use compression sacks anymore. Besides the risk to the insulation, these bags are heavy.

I always carry my insulation uncompressed- either in an XL stuffsack or at the bottom of my pack, depending on the time of year. I carry tiny packs sometimes with my light uncompressed quilts and insulation. In the winter, my large Golite Pinnacle is full and insulation fills the space.

Nothing wrong with packing the down into a sack for short periods but I don't go that route. I would if I needed to. But I would never again use a compression sack. I think it cut the life short on a Feathered Friends bag that I bought in college.

Doug

I'd rather not do that to my bags. They are all WM bags and cost over $300 each…..Nope I will not do.

I use a fairly large (13L) Granite Gear 'uberlight' cuben dry sack (0.57oz) for my down quilt which could fit into a bag as small as 5 liters. This is a lot lighter than a compression sack and it still allows you to adjust the volume. I normally don't roll the drysack too much so the down isn't too compressed, but if space is really tight then I roll the dry sack as small as needed.