Spark Pro Down Sleeping Bag (-9°C & -1°C)

Sea to Summit tests its sleeping bags for their temperature rating using the ISO 23537 test protocol.  This test gives two key ratings: Lower Limit and Comfort Rating. 

Lower Limit: The lowest temperature at which a man should stay warm.

Comfort Rating: The lowest temperature at which a woman should stay warm.

Sea to Summit Women’s-specific sleeping bags are listed using the Comfort Rating. Unisex bags are listed using the Lower Rating. For example, if the bag is rated at Lower Limit of 14°F | -10°C and Comfort rating of 27°F | -3°C, it should keep a woman warm down to 27°F | -3°C and a man warm down to 14°F | -10°C, if they are wearing warm clothes and using a good sleeping pad.

Remember: These ratings are just guidelines. Movement, weather, and your gear setup can all affect how warm you actually stay.

Pro Tip: Think of your sleeping bag, pad, and liner as a system. If you expect 28°F | -2°C weather, choose a sleeping bag rated for 23°F | -5°C, use a sleeping pad with an R-Value of 3 or more, and add a liner for extra warmth.