Fill Power and Maintaining Loft When Using an Over Quilt

My experience with my overquilt – 2.5 climashield, .67 shell and lining – is that the thing is so light that compression of the bag underneath is negligible. I would not consider that as a factor.

If I wanted to use a thicker overquilt, such that compression might occur, I would go for overfill with a high fill power down rather than going to a lower fill power. Let’s say you would have had 12 ounces of 950 in your quilt; you’d need 13 1/2 ounces of 850 to have equal fill. So instead of getting the 850, you get 13 1/2 ounces of 950. Now you have a warmer bag when you don’t use the overquilt, and plenty of density to handle the weight of a thick overquilt. But again, not needed in my opinion for a 2.5 apex quilt.

Not needed in a 100GSM overquilt with a 900FP but overstuffed inner bag but I think that if you were going thicker than 200GSM APEX then it would become a small problem, I agree with Paul above, overstuff by more than the usual 10%. I just did exactly that with my last sleeping bag refurbishment and went with 25% over fill

Thanks for the feedback, guys, very much appreciated~ I think I will go ahead with the 950 in that case. I don’t believe I’ll be using anything higher than 100 GSM / 2.5oz in an over quilt, as I don’t plan on going too far below freezing. Also, Edward, I was wondering where you went for your last sleeping bag refurb – the only source I’ve found so far that meets my needs is Nunatak.

Some numbers to play with:

Remember that fill power is cubic inches per ounce.  950 ci of 950 power fill weighs 1oz.

Spread over one square yard, that’s .73 inches deep.  2.5 of those layers is 1.8″ deep – and weighs the same as a layer of 2.5osy Apex.  So any loft of 950 thicker than 1.8″ will subject the remaining bottom layer to the same compressive load as if it had a layer of 2.5osy Apex on top.

Alternatively, you could think of that 2.5osy Apex as an additional 1.8″ of 950.

The point being, adding an over quilt doesn’t introduce the problem of compressing your insulation; that problem is always there.  It just gives you more choices about it.

Somewhere around here there is some conversation about how much lofting force different fill powers have.  Might be worth your while to see if you can find some of them.

Or just not worry about it :)

Hi Kyle
I am in Australia
I don’t think you want to post that far. But my bag was refurbished by the manufacturer, One Planet who were J&H back 30+ years ago when I bought the bag.
Lifetime warranty and fixed cost refurbishment available from them.

Regarding the compression of down:
Richard Nisley wrote quite a bit about the insulation decrease of compressed down in some posts on BPL from a few years back. He also backed his claims up with test results.

I am not entirely sure, but if I remember correctly, a volumetric compression of up to factor 2.5 had very little effect.

So in your case the overquilt would hardly affect the inner quilt.

Maybe try to search for his posts.

I use a 50 degree Apex quilt for my overquilt- it’s light (12 oz) and I notice no compression of down in my primary bag (FF Swift).

I would imagine if you used a really heavy overquilt you could see some, but I think most folks use a lighter overquilt. A 50 degree quilt adds ~ 20 degrees to your sleep system, don’t see a reason to increase that much

@dfranzen,

Correct:

“You can increase the aerial density of 800 fill down about 2.5x before it is becomes less thermally efficient than fully lofted down.”

Various threads about it here.

Thanks for pointing this out.

I wonder how that figure relates to fill power – what’s the limit for 950fp?