Formula for combining temp ratings on multiple bag/quilts

[BobCatMax]

As above really. How would you work out (roughly) the comfort limits on a combo..

Say +5 quilt with a +10 bag

Ta for the help, it's got me stumped!

[whitestone]

Not sure if there's a formula as such. There's a table on the Enlightened Equipment blog about layering quilts https://support.enlightenedequipment.co ... t-Layering that seems about right. You'll have to convert to sensible units

I've used a PHD Minimus 200 bag (5c) with a Cumulus 150 quilt (5C) at -6C and been fine.

[ianfitz]

Not sure if there's a formula as such. There's a table on the Enlightened Equipment blog about layering quilts https://support.enlightenedequipment.co ... t-Layering that seems about right. You'll have to convert to sensible units

I've used a PHD Minimus 200 bag (5c) with a Cumulus 150 quilt (5C) at -6C and been fine.

But it's very personal. I've used similar but with a 250 quilt and not been warm enough in similar temperatures. but I'm generally a cold sleeper anyway.

If you can work out the total amount and quality/fill of down it will give you a good start o working out temp ratings,

[Alpinum]

Warmth comes from loft, so if you lay your sleeping bag out on the floor, open it completely and put the quilt ontop of the part of the sleeping bag, which would cover you (you'll be lying on parts of the insulation, so you shouldn't consider that as loft) and measure the height of both, you get the loft height. Read it in meters.

Then you can use this:

17.5-3.5*loftheight in meters*100

A loft of 9 cm will result in a -14° C rating.
With baselayers and well fed it works really well for me (and others) and is the basis for when I make quilts myself.

[BobCatMax]

Not sure if there's a formula as such. There's a table on the Enlightened Equipment blog about layering quilts https://support.enlightenedequipment.co ... t-Layering that seems about right. You'll have to convert to sensible units

I've used a PHD Minimus 200 bag (5c) with a Cumulus 150 quilt (5C) at -6C and been fine.

that table is exactly the sort of thing I was after, thank you whitestone. I know it's not going to be the most accurate, but it certainly gives me an idea of what I should be looking at to get me down to 0°C

ianfitz, very true. I think I'm a boringly middle of the road kind of temperature sleeper.

Alpinum, that is very useful. Does that work for synthetic loft as well, or just down? (I'm guessing down). Slightly tangential, I'm trying to persuade my big sister in texas to send me some double black diamond quilts but she can't find anyone with a Costco card at the moment. I might ask for some advice/help in butchering them if they ever arrive.

[Alpinum]

Loft is loft - kind of. Works with any insulation.

Only that you could improve insulation in a static loft by using heat reflective elements or such with a weaker thermal conduction eg thicker and less breathable shell fabric.

But as far as I'm concerned, down is so stupidly light, if you want a warmer quilt or bag, just go with higher quality down or more of the same quality and choose the lightest possible shell for it. I've had over 150 nights in my DIY quilt with 7D Ripstop shell and it's still going strong. Same for my most used winterbag.

Of course, adding clothing, a bivy bag, a quilt or vapour barrier liner will improve the temperature rating and be cheaper and keep you more flexible.

For wintertrips between -10 and -20° C my girlfriend also uses a Rab bag with 500 g of 850 cuin down plus my DIY quilt with 220 g of 850 cuin down. She seems happy.

[BobCatMax]

thanks again, some really good info.

is there any school of thought on which layer inside which? I'm guessing synthetic outer, down inner?

[whitestone]

thanks again, some really good info.

is there any school of thought on which layer inside which? I'm guessing synthetic outer, down inner?

If you read the article I linked to, they recommend having the synthetic as outer then the dew point should fall within that layer where it has least effect rather than in the down.

[Alpinum]

thanks again, some really good info.

is there any school of thought on which layer inside which? I'm guessing synthetic outer, down inner?

If you read the article I linked to, they recommend having the synthetic as outer then the dew point should fall within that layer where it has least effect rather than in the down.

Very welcome.

I would do the same: synthetic as outer layer.

[BobCatMax]

Apologies Whitestone, I was blinded by the table!

Hmm, the quilt I had my eye on might not fit in the foot box of my synthetic bag. Mind you it packs down pretty small but I guess I'd be negating the effect of the loft