There are no standards for the temperature ratings on bags. Fit, features and loft all contribute to the comfort of the bag. A close fitting bag is warmer than a bag with a lot of extra room. A 20 degree bag has these features:

A hood,
Full collar - stops the bellows effect,
Draft tube - zippers cause a draft, and
Baffle construction - not sewn thru.

Bags degrade every time they are compressed. To measure the loft lay the top flat on the floor and allow it some time to fluff. Put a yard stick horizontally flat on top of the bag and push another yardstick vertically down next to it.


Comfort Rating in Degrees Fahrenheit Respective Loft Height in inches
40 1.5
30 2.0
20 2.5
10 3.25
0 4

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"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra