Sleeping bag down overfill: does it make a big girth bag warmer?

[Joe Meek]

I have on my floor right now a brand new Western Mountaineering Kodiak and brand new Feathered Friends Ibis EX.  Both rated zero degrees.  Neither have overfill.  Kodiak shoulder girth 66″.  Ibis shoulder girth 64″.  Kodiak hip and foot girths 1″ more than Ibis.

 

I wanted to compare these bags for many things but first I have an overfill question based on my at home test today.

 

I was in the Kodiak for 20 minutes.  I got very warm but not hot and my skin never approached getting damp.  I was in the Ibis 15 minutes and got hot to the point my skin was almost getting damp and I had to get out now!

 

Can overfill compensate for a bag that’s probably got too much girth for a particular user?  In this case would overfill have made the bigger girth Kodiak as hot as the smaller girth Ibis was after 15 minutes?

 

WM offers up to 4 oz overfill in the Kodiak.  But IIRC, WM said their overfill has negligible effect on inside girth.  This leads back to my question:  does overfill compensate for a bag that’s probably got too much girth to begin with?

 

Thanks to all who read and answer!

 

————————————————

Almost 70 yo now.  5′ 8″.  175 lbs.  On skin:  shoulder girth 46″, chest 44″, arms at side 52″.  Shirt: large.

 

Kodiak shoulder girth 66″.  Fill weight 30 oz.

 

Ibis shoulder girth 64:.  Fill weight 28.5 oz.

 

I wanted to compare these bags for:

 

1.  comfort of back sleeping position,

2.  ease/difficulty of turning onto sides for side sleeping position,

3.  for comfort in the side sleeping position,

4.  how hot I’d get inside each bag after 20 minutes.

 

I wore clean, freshly laundered lightweight merino bottoms and l/s zip neck merino top.  Lightweight cotton socks.  Lightweight merino beanie.  My a/c was on with indoor temp of 70 degrees and low humidity.

 

I was inside KodiaK 20 minutes.  I was very warm after 20 minutes but I never got hot.  By “hot” I mean to the point of damp skin and “I gotta get outta here now”.

 

I was very comfortable on my back and my sides.  Hood fit extremely well.  I closed top and bottom drawcords until only my nostrils and bridge of nose were exposed.  Neither top or bottom hood drawcord was tight against any part of my head.  Inside top edge of the hood rested lightly against my forehead and closed eyes, without any pressure or discomfort.

 

Kodiak neck baffles were uncomfortable at first because the drawcords strained across front and back of neck.  Moving the baffles around by hand and playing with drawcords relieved the tension while allowing full closure of top and bottom neck baffle and enough comfort that the cords, while still felt, didn’t bother me and after a bit, I didn’t feel them.

 

Still, this isn’t understandable in a bag made by guys who’ve been making bags since the 70s when we were listening to the Eagles and Stones.

 

After moving neck baffles by hand, the top and bottom baffle snugged and puffed up marvously.  That’s not a real world test in the cold, though; so I don’t know if any gaps existed that’d let cold air inside.  But it sure felt snuggly comfy at home.

 

I could easily turn onto my sides the Kodiak.  Once on my side I was a little more comfortable than in the Ibex because I had a little more room to put my left arm under my head (when on left side) and vice versa.  I had enough room to bend my knees and spread my feet; enough that I’d be as comfortable as one can be in a mummy bag.

 

I was very comfortable on my back in the Ibis.  After 15 minutes I was hot to the point my skin was almost at vapor point and I had to get out “now”!  What a difference 2″ makes (pun intended)!

 

With hands on chest in coffin position, my elbows made soft contact with both sides of the bag.  I couldn’t tell if the down was compressed but I don’t think it was.  I think my elbows were only contacting the inner shell and not poking into the baffles.  I’ll have to try that part of the test again!

 

I had enough room to move onto my side from my back without straining or stretching the bag anyplace.  I was comfortable on my side with just enough and a smidgeon more room for arm under head.  I could bend my knees and spread my feet enough that I felt I’d be as comfortable as any mummy bag would allow.  If I’d not been inside the Kodiak on my side I’d have felt the Ibex had a lot of room.  It did indeed have that room, but the Kodiak had a tiny bit more.

 

I don’t know if that extra leg room’s enough to make a difference.  I mean, really!  A “difference” to stretch out is 24″ or more!  Not 1″ in girth!

 

Right off the bat, Ibis neck baffles were much more comfortable than Kodiak.  Top nor bottom drawcord strained across my neck.  Even with front and back cords fully taut I never felt them on my neck.  I didn’t have to manually move the top or bottom baffles to be comfortable. Just snug ’em and be done with it.

 

Ibis hood definitely not as comfortable as Kodiak.  I couldn’t get hood to close to a tiny circle exposing only nostrils and bridge of nose.  When I did close hood as much as possible it closed to football shaped hole across my face, left to right.  The inner shell, while still lofted, was pressed uncomfortably against my closed eyes.  Enough that I could never sleep that way.

 

I futzed with the hood cords.  I stuck my arm out the bag and tugged the hood up.  Then down.  I re-futzed with the hood cords.  I could never get a round breathing hole, just a football hole.  Every time I got that hole small as could be, the inner shell pressed uncomfortable against my eyes.  I don’t think I could sleep, or sleep comfortably without waking, with the hood pressing against my closed eyelids.

 

I think it was Outdoor Gear Lab’s FF Snowbunting review that said FF’s hood wasn’t very deep and testers wished for a deeper hood.  Now I understand what they mean.

 

Today I learned the FF 64″ girth bag allows for comfortable back position, ease of turning onto side, and comfort when on my side.  I learned the bigger 66″ Kodiak is a bit more comfortable for those things.  I also learned 2″ girth difference makes a big thermal difference, much more than I thought.

 

For  me, the Kodiak’s extra wiggle room would be appreciated at my age.  But at 5F in a tent in the woods, the warmer Ibis might negate the wiggle room comfort of the Kodiak.

 

Going to ask WM the overfill question.  If overfill can make the Kodiak as hot inside my a/c house as the non-overfilled Ibex, I’ll take the Kodiak.  If not I’ll return this Ibex for an overfilled one and deal with the hood best I can.

 

My fingers are cramped now!

 

Thanks everyone!

[Dan]

Overfill will extend the life of the bag because it will retain loft better over time, as you lose down or the down becomes compressed. It’s not really intended to make a properly designed bag warmer.

[Disclaimer: I only read the first few paragraphs of the post, up to the line of dashes.]

[christopher witter]

The Kodiak uses 850+ fill power where the Ibis is using 900+ fill power. The smaller girth and the higher fill power are contributing to the warmer experience. Overfill would compensate making the Kodiak warmer then it currently is at the expense of a few ounces.

[lee kingry]

Hi Joe, I had the same concerns. And I went with the wider version of the badger Western mountaineering.

The two things that made a difference was never trying to make something not comfortable in your trials comfortable in your hiking it just doesn’t work.

And two the Western mountaineering allows you to maneuver the down to the top of the bag. And makes a very noticeable difference in warmth, and how quickly it will warm up.

A bigger girth bag is going to take longer to get to your comfortable temperature. But you can make that up with a few clothes inside if you need to because it’s that cold.

Just make sure you do the other things such as eat correctly Don’t be damp, and if you’ve been in camp in the cold for a while do some quick walking up and down the trail to build up a little heat prior to getting in the bag. And there’s always the hot water bottle or sock wrap stone.

But definitely go with the bag that’s more comfortable while you’re testing.

[Joe Meek]

Christopher W;

 

Not so sure overfill will make bag warmer.  I’ll still have the same interior space to warm even with overfill.  If I couldn’t warm the space inside my 70 degree house, not sure I can warm it at, say, 10 degrees, even with max overfill of 4 oz.

 

Long ago WM told me overfill has negligible effect on interior volume.  Yesterday I emailed WM asking if overfill will make it easier to warm that same interior volume.

[Joe Meek]

Lee;

I tried the FF with hood cinched three times.  I could get it comfortable if I pushed some of the down around by hand.  But when I rolled to my side I had to do it all over again.

I agree.  If it’s a pain now, it’ll be 5x more a pain on a cold degree night in the woods.

Two winters ago I froze all night in a WM Terralite.  It’s rated 25 degrees.  Low temp that night was 27 degrees.  Shoulder girth is 1″ less than the Kodiak.  Hips 10″ more than Kodiak.  Foot 2″ more than Kodiak.  I think the hip girth is what did me in.

I used Thermarest XTherm large/wide pad.  I wore midweight merino top/bottom/beanie/socks; EMS puffy (8 oz fill); and Integral Designs (synthetic fill) puffy pants.  I warmed the bag with Nalgene hot water bottle.  And I was very cold all night long.

Long ago WM told me overfill has very little effect on interior volume.  Yesterday I emailed them asking if overfill would make that same interior volume faster to warm up.  Seems to me that no matter how much down you have, if the space is too big for your body to begin with, you’re not gonna warm that space any faster or any warmer, no matter how much down you have.

But I don’t know that for sure.  Hope WM can answer for me.

[Joe Meek]

Shifting down to the bag’s top works best for back sleepers who don’t turn onto their sides during the night.  If you shift down from bottom to top of bag, then eventually turn onto your side during the night, your back will be cold or, less warm, than your front.

I think that’s where it’s said overfill shines, because it mitigates if not prevents down shifting inside the baffles.

[bradmacmt]

The Kodiak uses 850+ fill power where the Ibis is using 900+ fill power. The smaller girth and the higher fill power are contributing to the warmer experience. Overfill would compensate making the Kodiak warmer then it currently is at the expense of a few ounces.

Western bags are typically around the 900 fp range, they just prefer not to overstate their bags fill power. FF has no issue overstating anything. I’ve always found WM bags “loftier” in side by side comparisons. FF bags are great, I just prefer WM’s more transparent and conservative approach to bags. Heck, FF doesn’t even provide loft figures!

The reason you felt warmer in the FF bag could be you got in the WM first and got your body revved up, then you slid into a slimmer bag and your body did the rest.  My default is always to a slimmer bag – for me they just “sleep warmer” than a bag of equal loft, but wider girth.

Aside, I’ve owned quite a few WM bags over the years, and have always gotten overfill. As was mentioned, it’s not an extra warmth thing (though WM says it adds a bit of warmth), but rather it’s a longevity thing.

[Author]

Posts