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Backpacking Quilt Temperature Ratings

Thermal images of a quilt with box baffles and a quilt with sewn-through baffles. Photo courtesy of Therm-a-Rest.
Thermal images of a quilt with box baffles (left) and a quilt with sewn-through baffles (right). Yellow areas indicate heat leakage. Photo courtesy of Therm-a-Rest.

An Interview with Therm-a-Rest’s Quilt Team

How much can you trust the temperature ratings that gear manufacturers give their backpacking quilts when there isn’t any standardized way of measuring them, like there is with sleeping bags? Why do some people sleep colder in quits than others? What are some of the other variables that can affect your comfort level and warmth when you sleep with a quilt? These are important questions for backpackers who want to compare quilts from different manufacturers or want to improve their sleep systems so they can be more comfortable at night.

I recently spoke with Kyle Thackray and Greg Dean, both from Therm-a-Rest, about how they assign temperature ratings to their backpacking quilts, and the other aspects of quilt sleep systems that have the greatest impact on the user warmth. Therm-a-Rest is a engineering-driven company and they take a very scientific approach to this problem which I think you’ll find instructive.

Here’s a summary of our conversation. The questions were mine, but I’ve paraphrased their responses below for readability. Any errors in translation are my own.

There aren’t any industry standards for measuring the temperature ratings of backpacking quilts, like there are with sleeping bags. How does Therm-a-Rest assign temperature ratings to their quilts and how reliable are they?

We test our quilts the same way we test our sleeping bags, by sending them to the testing lab at Kansas State University. They use the same test setup defined by the sleeping bag temperature rating standard to test our quilts, using a mannequin dressed in long underwear and lying on a sleeping pad with an R-value=4. Since quilts do not have mummy hoods, we put an insulated hood on the mannequin, because we assume that users will wear an insulated hat or hood when they sleep with a quilt. We’ve found that wearing a down hood will raise a quilt’s temperature rating by 4 degrees, while wearing a fleece hat raises it by 2 degrees, compared to wearing no headwear at all.

Are there any standards efforts under way or in discussion around standardizing the way that quilt temperature ratings are measured?

Not that we are aware of. Part of the reason is that most backpacking quilts are made by small companies that don’t have the where-with-all to invest in a standards definition process. But we expect that a standard will evolve as larger companies and retailers, including REI, start making and selling more quilts.

It’s well understood that men and women need different amounts of sleep insulation. How are gender differences reflected in the temperature ratings that Therm-a-Rest assigns their quilts?

We view it more as a function of body size than gender. The most important thing for men and women is to have a quilt that fits you properly. You don’t want one that is too long or too narrow, so that the edges lift up and let in drafts when you roll around at night. We’ve found that the regular sized quilts sold by many of the cottage quilt brands aren’t wide enough for most people, so we’ve significantly increased the width of our quilts, including the new Vespers.

Can back sleepers and side sleepers expect the same kind degree of warmth from a quilt or will one sleep colder than the other based on their sleep position?

As long as there are no side drafts and the quilt is tucked up around you, there shouldn’t be any difference.

What are the most important features besides the quantity of insulation in a quilt that can affect its temperature rating?

Fit is the most important. You don’t want a quilt that’s too long for you. The pad attachment system is important to eliminate drafts from entering. Perimeter draft tubes are also effective, as well as draft collars around the upper chest and neck that can be fully closed with a snap or a draw cord.

What about baffle construction?

Box baffles are the warmest and that’s what we use on the  Therm-a-Rest Vesper Quilts (32 and 20), which are fully box baffled. There will always be cold spots with baffles that are sewn-through. We use a thermal imaging camera to study different design options and find where heat is escaping (See top photo).

Are Therm-a-Rest quilts designed for ground sleepers or can they also be used in hammocks.

They’re primarily for ground sleepers, but the pad attachment system is removable, so there’s no reason they can’t be used in a hammock.

Is there a formula for estimating how warm you can expect to sleep by layering two quilts together. For example, if you stack a 40 degree quilt over a 20 degree quilt, what is the lowest external temperature you can expect to be comfortable in?

Sort of, but it’s very hard to generalize because it depends on the specific quilts and how their insulation is distributed. It’s also based on clo values and not temperature ratings, which makes it hard to translate for general use.

What is more effective in term of blocking drafts, a pad attachment system or an ultralight bivy sack?

A bivy sack would be better at blocking drafts, as long as you don’t shift off your sleeping pad at night. Of course a bivy sack is also heavier, whereas the Synergy link system that comes with our Vesper quilt only weighs 3 grams.

At what temperature would you switch from a quilt to a mummy sleeping bag, in colder weather.

For me (Kyle) personally, I switch when it drops below 20 degrees (Fahrenheit). We also find that it gets increasingly difficult to convince people that they’ll stay warmer in a quilt below 20 degrees, no matter how good the pad attachment system is. But a lot also depends on the kind of sleeper you are. If you move around a lot at night, there’s a higher likelihood that you’ll experience drafts. When it’s colder than 20 degrees outside, drafts have a much higher impact on your comfort.

Philip: Thanks guys. I appreciate the background information and think my readers will find it informative.

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  1. Nice interview – thanks, Philip.

    I’ve used Thermarest’s 650-fill Corus quilt for several years, and found it good down to about 50; I think it would work down to 40, but didn’t want to try to push its limits (in the woods, “pushing its limit” is a euphemism for “I’m cold.”)

    I recently upgraded to the 900-fill Vesper 32, but haven’t had a chance to try it out yet. (It’s been in the 20s here, below the quilt’s rating, and raining and snowing, and I’m not willing to spend two days cleaning and drying muddy gear just to see if the quilt’s rating is accurate.)

    I didn’t replace my 650 fill down sleeping bag yet, but I’m hoping it can find a new home based on the hope that the quilt’s rating is accurate. (I don’t intend to go out when the predicted lows will be below about 40 anymore; my “I can sleep at 5 below” T-shirt is still in good shape, and doesn’t need replaced.) Thermarest calls this the Vesper 32, which connotes its Limit rating of 32 degrees (that’s the rating at which you’ll be cold, but won’t actually shiver uncontrollably.) The Comfort rating (you’ll feel warm in long underwear) is 40. My plan is to carry down pants and hooded down jacket (Montbell’s Superior Down models) which I’ll use to stay warm in camp, then wear to bed. I’m hoping this will lower the Comfort level to about 32, to give me a bit of safety margin in case it gets colder than predicted. (The Vesper, plus the down pants and jacket, weigh less than my current down bag, which is about two and a half pounds and rated to 20.)

    The interview didn’t touch on sleeping pads; if you’re using a quilt, the pad is critical. Since I sleep a bit on the cold side, I use the r-5.7 Neoair XTherm Max. (I’ve read reviews that say the XLite is all you need in the conditions in which I intend to use the quilt.)

    I’ll try to remember to tell you how this works after the weather breaks and I can get the right temperature range to test it. I’m really interested to see if this quilt is all I’ll need for what I intend to do.

    • Actually it did touch on sleeping pads. It said that their rating depends on using an R value of 4. People who try to get by with less probably won’t be able to achieve the stated temp rating. The same holds for sleeping bags.

      • I got to test the Vesper 32’s rating this weekend. I wore midweight longjohns and Montbell down balaclava, and added Montbell Superior down pants and jacket as the temperature fell to its 25 degree low; I was cozily warm all night. There was plenty of width to reach the ground on both sides of my XTherm pad, and the ability to snap it closed around my neck and cinch down the draft collar sealed the deal.

  2. Wondering if there’s a typo. Should it say “sleeping bag” instead of “quilt”?

    “We also find that it gets increasingly difficult to convince people that they’ll stay warmer in a quilt below 20 degrees, no matter how good the pad attachment system is.”

    • Oh, I see it now (I apologize, I missed it the first two times I read it.) I’d agree that a lower-rated pad will affect the ability to achieve the rated comfort; would it be fair to say that the opposite is also true: that a person on a higher-rated pad might feel the rating is slightly conservative? (A warmer pad might not be a game-changer; the limiting factors are still going to be the loft on top of you, and the lack of a hood if you don’t wear a separate hood or hat.)

    • No Iago. That is correct. They can’t convince people that they’ll stay warm in a quilt below 20 degrees.

  3. It is valuable to hear a major outdoor gear manufacturer state the following on insulation, “We view it more as a function of body size than gender. The most important thing for men and women is to have a quilt that fits you properly. ” Such a simple concept is often ignored for women. The value of a properly fitted sleep covering for women would include recognition of average shoe size, hip and shoulder proportions, average height, etc. Stating the obvious , an ill fitting piece of equipment equals weight and performance penalties. As well as providing wider quilts, how about a quilt proportioned for women? Maybe an XTherm pad for women using the same proportions as the very successful NeoAir XLite womens model?

    The durability and comfort of the Thermorest NeoAir Xlite womens’ pad is truly outstanding! When a manufacturer produces such a stellar piece of equipment, one hopes they continue to prosper in this dimension.

  4. “wearing a down hood will raise a quilt’s temperature rating by 4 degrees, while wearing a fleece hat raises it by 2 degrees.” My experience with three EE quilts has been the claimed temp rating can’t be reached without a puffy hood similar to that which you would find built into a same rated sleeping bag. I suspect many people are turned off by quilts because they expected their thin wool beanies would be adequate for the rated temperatures.

    • That’s why people should be asking EE (and other quilt vendors) how they assign temperature ratings to their quilts including assumption about headgear and sleeping pad R-values. I think the Therm-a-rest guy’s methodology is pretty sound and its nice that they’re so above board about it.

      What I also find important, no essential, is to consider the entire sleep system around the quit including the hood, long underwear, attachment system, and pad. Optimizing the weight of one buys you less than you think.

      • I thru hiked the AT in 2018 with 2 EE quilts, one rated at 20 degrees and as it warmed up I purchased a 40 degree quilt. I also used a Thermolite Reactor liner that was supposed to add 10 degrees to the rating at any temperature below 30 degrees I was on the cold side. In the low twenties I was very cold. A few nights in the teens left me shaking! And I had a Thermarest Xtherm pad. And on the coldest nights I had every stitch of clothing on.

        I have a large assortment of sleeping bags that have always felt performant to their ratings. I didn’t feel this way with quilts. Despite that I really appreciated the lightweight and roomy feel with quilts. My advice to any quilt buyer is to note the temp ratings aren’t accurate and purchase a quilt with a lower rating than you would otherwise.

      • Here’s how they assign the ratings per their website. Like I said, most sleepers need proper head covering for the ratings to be accurate.

        …….. “For testing, we sent the 20°F and the 40°F Revelation down quilts to the Institute for Environmental Research at Kansas State University. They use a heated manikin dressed in thermal underwear, socks, and a face mask. When our quilts are tested, the manikin also wears a Hoodlum; this is essential to get an accurate rating, or all the heat loss would occur in the head area. When using a quilt, you should be wearing a hood or hat as well.” ……

  5. What would you take away from the answer on stacking? Which source do you give more weight to; that answer or Enlightened Equipment’s which has a nice chart posted?

    • I’d give more weight to the Therm-a-rest answer because I’ve spoken to a person who’s studied the issue with sophisticated testing equipment as his disposal and explained to me the difficulty of converting clo measurements to temperature ratings. I haven’t had a conversation with Enlightened Equipment about the issue, so have no way to assess if they’ve done similar due diligence.

      Temperature ratings below 20 degrees are extremely variable, which is why the sleeping bag standard doesn’t cover them. I would imagine quilt temperature ratings have a similar problem, so I’m surprised that Enlightened Equipment has found a way to eliminate the statistical issues for predicting temperature ratings for quilt stacking combinations under 20 degrees. They should patent or copyright it.

      • Good point Philip! That does smell fishy.

      • Agreed, although Therm-a-rest’s answer was really a non-answer, it reinforces my skepticism with EE’s chart.
        I’m camping(hammocking) this weekend and stacking quilts. According to EE’s chart, my 20 degree and 30-degree underquilts should take me to -20.
        No knock on EE’s stuff, which I’ve used and it’s fine but my quilts are better imo (overstuffed Hammock Gear Incubator and 30 degree Feathered Friends Flicka) but I would not bank on what I’m stacking to go below 0 much less EE’s.

  6. My GF and I stack quilts for Winter hikes/camping trips. Easily gets us down to 0 with 30 degree single quilts and a 20 degree EE Accomplice draped over the both of us wearing baselayers and a Hoodlum. For much below zero, we have some -30 degree bags from Eddie Bauer that are overkill and bulky and heavy. Three quilts are much lighter and equally warm.

  7. Thanks for the terrific post, it was a great topic. The information that you obtained from the Therm-a-Rest guys was invaluable to anyone who might be considering the purchase of a quilt.

  8. Thanks for sharking the interview!

    If I had a chance, I would have asked them about the 2016 NIH study which specifically criticized the current standards for only calculating for “global thermal comfort”, and not addressing localized thermal comfort in the feet.

    (From the Abstract): “However, all these models calculate the global comfort and limit temperatures, i.e., these models only considered the whole body thermal comfort. It seems that both the comfort temperature and the limit temperature defined by the models failed to take care of local thermal comfort in the feet”

  9. The only good argument for stacking quilts: I don’t own a winter bag :)

  10. Another excellent interview with valuable data-based answers, keep it up. They’re probably right that some quilts are too narrow, but I think in a hammock you can get away with a less wide quilt because of the way the under quilt should be wrapping up partially around you from underneath. At least, that’s been my limited experience. I have a harder time staying warm in the same temperature in my bridge hammock versus my gathered end, using exactly the same quilts, and I’m thinking it’s because of the drape/width issues (meaning the bridge is wider and acts more like a cot while the gathered end snugs up tight and helps wrap me in downy goodness).

    I’ve read a bit about Clo values but not enough to do more than ask questions like: don’t the Clo values sort of break down at very, very low temperatures? I’m pretty sure the additional layers don’t add up in a linear way, more like a curve that’s heavily dependent on the temperature as well as the temperature rating of the quilts being stacked. Any chance you will interview somebody about that subject, or is it too nerdy?

  11. Good article Phil ! Just curious have you reviewed the hyke and byke quilts or sleeping bags they are a lot cheaper than others and looks like good quality I just can’t find any reviews from other hikers yet and your opinion means a lot into what I might purchase. Thanks for your website it’s pretty kickass , about the only email I actually read

  12. I just tried my western mountaineering mega light mummy bag with a paper thin BPL summer quilt as a liner; was warm as toast down to 20*F in a summer style tent (MSR zoid 1.5). Using an old but still good camp rest self inflate. Tried the same bag/ quilt again with an exped Hyperlite stacked over a 20 year old Z-rest pad and absolutely froze; almost didn’t last the night. Third night I stacked a klymit static v insulated over the Z-rest and was quite cold on the bottom but OK cold not frozen.
    I am hugely impressed with the warmth and comfort of the 20 year old camp rest pad and seriously doubting the shoulder season “stretch-ability” of 3 season pads for winter temps. The night I froze I barely got through the pre dawn chill by putting the z-rest on top of the exped. Warmer but hard to keep in place and neither comfortable nor recommended.
    Tonight I’ll be switching the out the summer quilt for a VBL liner and see how that stacks up.

    Over all impression on using a summer quilt as a bag liner is that it’s fantastic for weight and versatility if, and only if, the there are no flaws in the rest of the system and the individual components fit correctly when stacked, ie a narrow quilt that fits inside a wide bag that fits on top of a pad that’s fully adequate for target temperature.
    All tests performed on 20*F nights wearing Costco $9.00 long underwear and a wool ski hat.

  13. I was contemplating purchasing the short Nemo insulated sleeping pad. They do not give an R rating but they state it is good for temperatures between 10 and 20 degrees. I also checked out Neo Air Xlite short and they give a R 3.5 for theirs. Would these two be somewhat equal? I am hiking the AZT in early March starting South and was trying to cut 8 ounces off my pack weight by not taking my Neo-Air R 5.2 which weights 16 ounces. The night tempts will be in the 30s average and getting warmer as i head North. I have two quilts one is a 35 degree MLD and the other a 20 degree Nunatak. I will be taking the 35 degree quilt.

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