How much loft for 15F? (Down)

**Frost** · 01-29-2012, 23:21

The last number I need to lock down on my new down UQ for my bridge hammock is exactly how much loft I'm going for. I have somewhere in the neighborhood of 30oz of down, and my quilt is going to be 60"x40".

I'm aiming for something in the 15F range, as this is as cold as my mummy bag/TQ will happily go without some augmentation.

By my figuring, with 20% over stuffing, I should be able to get at least 5" of loft (assuming this down is 550fp). Anybody care to wager if this would be enough to get me to that magical 15F mark?

**catalyst** · 01-30-2012, 00:25

You don't need to use even close to all that down. This is the chart I use for loft. (scroll down) So lets say you need 3" of loft for 15 degrees.

60 * 40 * 3 / 550 fill power = 13.10 ounces of down needed
13.10 * 20% overstuff = 15.7 ounces of down

Using 16 ounces will likely give you more loft than just 3 inches. I think you'd be set with that amount. Five inches of loft would get you well below zero.

**MAD777** · 01-30-2012, 11:14

I agree with 3".

**TinaLouise** · 02-06-2012, 08:15

What is the ending measurement of your baffel height? (meaning... after you sew in your baffels, what will their height be?)

**BillyBob58** · 02-06-2012, 08:58

As Catalyst posted, 3" should be plenty and 5" should go well below zero for most people, as an average. For example, a JRB MW3 UQ has 3" loft and is rated at 15-20F, an MW4 has 4" and is rated 0-5F. But as you know, people vary greatly, so you will need to plug in what you know about your individual cold tolerance.

Also keep in mind, these loft ratings have been developed over the years using sleeping bags, with which drafts and gaps are not normally a problem. So the above ratings are made with the assumption that fit is about perfect. There are lots of things that can go wrong with a quilt(drafts), and things can be even trickier with an UQ(gaps/drafts). Getting the UQ snug enough on the bottom and ends to avoid gaps/drafts but not so snug as to compress loft enough to loose insulation can be tricky. A differential cut seems to make controlling that much easier, you don't have to worry so much about getting things too snug.

But if fit issues are well controlled, you have enough head warmth and you keep it dry, 3" of loft should do you. If you are a super cold sleeper, you might want a tad more or some extra poorly compressible layers of clothing. This would work fine for me, but not my wife or daughter. In the house or car, they complain of being quite cold when I am more than warm enough. Temperature control is a constant conflict. I have seen a girl be cold in a minus 5 Marmot bag in a 2 person tent when it was maybe 25-35*F.

**Knotty** · 02-06-2012, 13:17

BillyBob58, you are the voice of reason!

Just because a particular loft goes to 15ºF in a sleeping bag doesn't guarantee it will with a TQ or UQ for all the reasons you give.

**BillyBob58** · 02-06-2012, 13:27

Originally Posted by Knotty

BillyBob58, you are the voice of reason!

Just because a particular loft goes to 15ºF in a sleeping bag doesn't guarantee it will with a TQ or UQ for all the reasons you give.

Thank you Knotty. Now I personally have had no trouble being nice and warm close to the ratings of my Dif cut JRB quilts,(and probably beyond if it would ever get cold enough here to test), UQs which seem to be rated according to the above table, more or less. But as you note, no guarantees due to so many variables.

**Boothill** · 02-06-2012, 13:59

does anyone know if loft of any height, say 2" has the same warmth rating for any given down fill power.......

ie: does 2" of loft from 550fp have the same warmth as 2" of loft from say 800fp, i know the weigh will be different just wondering if the temperature rating is different when using better down when the loft height is exactly the same

i've always assumed it would be the same, but don't know for sure

boot

ps: sorry for the hijack

**lmoseley7** · 02-06-2012, 14:13

Originally Posted by Boothill

does anyone know if loft of any height, say 2" has the same warmth rating for any given down fill power.......

ie: does 2" of loft from 550fp have the same warmth as 2" of loft from say 800fp, i know the weigh will be different just wondering if the temperature rating is different when using better down when the loft height is exactly the same

i've always assumed it would be the same, but don't know for sure

boot

ps: sorry for the hijack

I think this is an interesting question. From my research here on the forum I would guess the knee-jerk answer would be that the only difference in using sub-par down would be that it would weigh more, but there have also been discussions on the law of diminishing returns of overstuffing down. If it takes more down to expand to take up the same amount of room, wouldn't it be similar to too much overstuff? Maybe the issue with too much overstuff is that at some point you are adding weight with little to no increase in temp rating, not that by overstuffing that the rating decreases. I'm interested in hearing from the experts on this.

**TinaLouise** · 02-06-2012, 16:39

I too would think that 2" of loft would be the same reguardless of the rating of the down. I think this because to get to the 2 inch loft, you'd have to use more of the lower rated down and less of the higher rated down, just so it would loft to the correct height. If you look at low rated down and then compair it to higher rated down, you can see that the higher rated stuff puffs out way further. You do have to be careful with any down, that you don't over stuff it so much that the "puff-ability" is restricted by adding to much. And on the reverse side, that you've not done the math right and that you don't put enough down in your quilt and you have air pockets.