Sleeping bag fabric must perform a number of roles: keep the fill in the bag; allow body generated moisture to get out; and the shell fabric must also keep external moisture out in some conditions.
Fabrics that are ‘downproof by construction’ are ideal as they don’t use coatings which can reduce breathability: instead, the very tight weave prevents down from escaping.
Vapour Vent (V2)
Vapour Vent (V2) is used as the inner in all One Planet sleeping bags and as the shell for most. This durable, tightly-woven fabric is ‘downproof by construction’: the weave is so tight down cannot escape through the cloth. Coatings are not required, so body vapour can vent through the fabric more effectively, reducing moisture build-up in the down and allowing it to loft to its full potential. We use three weights of the silky V2 fabric, differentiated by their denier. (The fineness of thread is measured in denier: the finer the thread, the lower the denier and the lighter, more silky and expensive the fabric.)
The Winter Lite and Bush Lite are designed for extreme conditions, so we have chosen their shell fabric accordingly. Pertex® Endurance is the lightest, most breathable and weather-resistant fabric we can find. It weighs a measly 36 g/m2, has a water head of 1000 millimetres and a breathability of 7000 g/m2/24 hours (according to results from test JIS L 1099 A-1). You do the comparisons: it’s hard to beat! The fabric combines an air-permeable membrane with a durable nylon face fabric: the membrane is so thin it barely affects the weight or softness of the material, but it is highly breathable and water and wind resistant.