WM Pod 15 & Pod 30?

With 2.8″ average single layer loft, this bag is conservatively rated. The average sleeper should be fine to about 0F with an adequate pad.

Richard,

Do you mean 0 degree Centigrade, not F?

Cheers,

0F not 0C.

Interesting. WM rates the POD 30 to 30F.

I see their new Summerlite bag is rated to 32F.

I own a POD 30, and like it. I feel its generally on its rating of 30 degrees. I know when it went down to 25 with an Micropuff, I started to get a little chilled, but I have been sleeping cold lately.

WM POD30. Great sack. Good temp rating IMO. I’ve used the POD 30 for ~1,000 miles of hiking in the desert during Sept-Nov. Happy with its performance. I did cut off the ‘pad sleeve’ on the bottom which reduced the weight and increased the function in terms of useable range of temp. Combine with a WM Down J and a balaclava, and I’ve been good to 20F. I should note that I purchased my POD 30 the first year of production so some things may have changed since.

Brian

I have a Pod 30 and would say its comfortable to 40 and usable to 32 with other insulation. I like it.

I just got and used my WM Summerlite. It was on an island in the middle of Lake George, NY and it got down to, yes 32 degrees that night. Warm and toasty I was! I was in a very large tent with some breezes coming through and still would have been toasty down to 20 I feel. Great Bag, fits me close but not too snug.

Yeah, I’ve found the rating of the POD 30 to be pretty accurate for me, but no way it would go to 0 F without some serious extra insulation on.

Dear Anonymous,

In my original post I said, “With 2.8″ average single layer loft, this bag is conservatively rated. The average sleeper should be fine to about 0F with an ADEQUATE PAD.”

First take a look at BPL’s own recently published “Backpacking Light Position Statement on Sleeping Bag Temperature Ratings”. The POD30 has an average loft of 2.8” and the BPL table lists the temp rating as 10F = 2.6” and 0F = 3”.

I did my analysis independent of the BPL analysis. I will now explain my reasoning:

The average insulation used in this type of sleeping bag averages a W/mK of approximately .042 which is equivalent to a .605 m2K/W value for 1” of insulation. Since the POD 30 averages 2.8” (as measured by BPL) this yields a total m2K/W value of 2.8 * .605 = 1.694 m2K/W.

Based on instrumented physiology tests using average males of 154 lbs in their mid 20s, a 3/8” foam pad, and .6 clo of clothing (equivalent to medium weight long-underwear), 1.694 m2K/W provided adequate comfort to -9F. The tests were done by the US Army Quartermaster Corp.

The Army QM testing information led to my assertion that this bag should be adequate to about 0F with an “ADEQUATE PAD”. The pad provides the large margin that makes the difference between adequate thermal comfort and total thermal comfort as well as addressing the lower basal metabolic rate (BMR) of women, skinny folks, and older folks. Assuming you sleep on your back approximately 40% of the total sleeping system insulation is provided by your pad. Pad insulation that closely matches the insulation of the bag can be provided by options such as the Exped Down7, the Stephensen DAM, etc. As an example, the Exped7 weighs ~1.5 lbs, is 2.8” thick (same as the bag), and provides an R 7.3 insulation value versus the Army test pad which is a 3/8” closed cell foam pad with an R 1.6. What is the R value of the pad (bottom insulation) you used to make your temperature rating assessment?

Improper storage or improper moisture management can dramatically reduce the loft of a sleeping bag. The average loft for this bag, as measured by BPL, is 2.8”. What is the loft of your bag that you used for your temperature assessment?

Forced convection (wind) can dramatically lower the insulation value of a bag. Is your temperature rating based on the use of your bag in an enclosed shelter or bivy that blocks the wind?

The difference in BMR and can also affect your perceived sleeping bag warmth. Women sleep colder as do skinner folks and older folks. Do you fall into one or more of these categories?

Richard or anyone,
I’ve seen the unit “clo” used in these forums before but haven’t seen a definition. I hope this isn’t a stupid question, but what’s a “clo”?

Eric writes:

>> I’ve seen the unit “clo” used in these forums before but haven’t seen a definition. I hope this isn’t a stupid question, but what’s a “clo”?

A Clo is unit of thermal insulation originally developed for clothing. One Clo is the insulation required to keep a resting person warm in an indoor room at 70 deg F — about the insulation provided by a business suit. Quantitatively, one clo is equal to 0.155 m2K/W.

Cheers,

-Mike

I am a female who sleeps on the warm side, if anything. I use a Stephenson’s DAM. I have certainly slept comfortably in my POD 30 well below freezing, but wear down socks, jacket and balaclava when it gets that cold. I’m pretty sure the POD 30 would keep me alive down to 0 F, but I doubt that I would be comfortable without the extra clothes. I also think the comfort level of the PODs depends on how you sleep. my partner is a side-sleeper and doesn’t find the bag as warm as me (a back sleeper) but I think that’s from cold sneaking in through the bottom when you roll on your side.

My bag is stored fully lofted, dry and shows no sign of compression.

But most of all, I am comparing the POD 30 to the many other bags I’ve used, from very warm full winter weight bags to Arc Alpinist. I think the PODs are more conservatively rated than many other brands, but that’s true of all WM bags IMHO. For instance, using the Army QM testing equation, my Arc Alpinist (3 inch loft)should be much warmer than the POD 30, yet I don’t find it to be nearly as warm, even with a thick down balaclava on. So there is a lot more to the equation than just loft. I love my POD 30 and use it most of the year, but I wouldn’t personally push it to sub-freezing temps without extra insulated clothing on.

Dear Ms Anonymous,

Thank you for your polite and comprehensive explanations. Based on this information, I think I can explain why our assessments were slightly out of sync.

Although the Army QM data didn’t make the distinction between men and women, the European Union’s EN 13357 standard does. I looked up the EN13357 Comfort Standard Man and EN13357 Comfort Standard Women for the insulation value of the POD30. Note that the EN13357 data for men and women more widely diverges the colder the temperature. At the POD30’s insulation value, the EN13357 data shows a slightly higher temperature rating for Women and slightly lower temperature rating for Men than does the simpler Army QM data. The difference between the two EN13357 ratings is approximately 18F for the insulation value of the POD30.