Thermarest saros three season synthetic sleeping bag northern light our most versatile three season synthetic sleeping bag just got better the three season saros sleeping bag is the perfect choice for backcountry trips that start with a shaky forecast now redesigned with thermacapture tm seams to boost the bags warmth without adding bulk the saros includes our eraloft tm synthetic insulation which is quick drying and weather resistant making it ideal for backpacking and mountaineeri