Design and Tech


Differential Cut Shell & Lining

Down insulates best when it is uncompressed and fully lofted. To help the down loft correctly we use a differential cut shell and lining. The top shell of all Sea to Summit sleeping bags is cut larger than the lining. This creates space in between for the down to loft fully. In addition we use 3D side walls which gives the distinctive vertical sides to our sleeping bags which further aids vertical loft along both sides of the bag. In the bottom of the bag we use a reverse differential cut. By increasing the size of the lining relative to the shell, down lofts up to fill the voids around your body, torso, legs and the small of your back. Trapping heat close to the skin is essential for efficient warm sleeping.

Offset Baffles

Offset baffle construction provides a stable structure that allows the down to loft to the correct density and minimizes loss of heat through seams. This improves thermal efficiency of the sleeping bag without adding the weight of a more complicated baffle construction.


Side Block Baffle & Fill Ratio

The loft is optimised using a side block baffle construction which allows the bags to be filled with a different ratio of down in the top and bottom. We have put more down in the top of the bag where it is most effective as the down isn’t compressed by your body weight. The exact ratio of down fill must be matched to the shape of a sleeping bag. The Micro and Spark bags’ slim fit forms a tight cocoon around the body which rotates with you when you toss and turn at night. For this style of bag it is best to use a 55/45 (top/ bottom) fill ratio. In the Alpine, Traverse, Talus and Trek bags a 60/40 fill ratio is more suitable. These bags are a generous cut and have room inside to rotate without the bag following.