Circuit Down Sleeping Bag

Like other quality sleeping bag manufacturers, Sea to Summit tests its sleeping bags for their temperature rating using the ISO 23537 test protocol. This information is presented using the following icon:

The test produces a Lower limit (the temperature a male sleeper should use for orientation) and a Comfort Rating (the temperature a female sleeper should use for orientation). Both are printed inside the sleeping bag and published in the Tech Specs of the sleeping bag webpages.

Sea to Summit Women’s-specific sleeping bags are listed using the Comfort Rating. Unisex bags are listed using the Lower Rating.

What you need to know about the test

A unisex sleeping bag with a Lower limit of 14°F/-10°C should keep a male sleeper comfortable down to 14°F/-10°C provided the sleeper is dressed in heavyweight base layers & insulating cap, and uses a sleeping pad with an appropriate R-Value (for these conditions, at least 4.0).

The same bag will have a Comfort Rating of around -3°C/27°F, so a woman with the same base layers, cap and sleeping pad would be comfortable down to an air temperature of -3°C/27°F.

These numbers are guidelines, not guarantees. Many factors affect the actual performance. The biggest variable is that the test manikin does not move, where a moving sleeper can draw air into a bag, or compress insulation.

Example

It’s important to think of a sleeping bag, sleeping pad and a liner as a sleep system – combine individual products appropriate for the conditions, and the system will provide the best possible night’s sleep.

If you plan on sleeping in air temperatures of -2°C/ 28°F, choose a sleeping bag with a gender-appropriate rating of -5°C/23°F, add a sleeping pad with an R-Value of 3+, and use a Reactor Liner.