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?