All Spark sleeping bags feature ultra-light weight, minimal pack size, and excellent thermal performance. In the Spark SpII, continuously sewn vertical chest chambers contain an extra amount of down, reducing cold spots. Additional continuously sewn horizontal chambers in the foot area minimize weight. A half-zip with two sliders allows for easy entry and provides additional ventilation. The optimized sizes of Spark sleeping bags offer more space at the shoulders and hips. The integrated zipper channel prevents heat loss and for added protection, the SpII comes with a thermal collar.Ultra-Dry DownUltraDry Down is a PFC-free, water-repellent down treatment used in all Sea to Summit sleeping bags. UltraDry Down retains over 60% more fill power, absorbs 30% less moisture, and dries out 60% faster than untreated down - meaning the down insulates better even when damp. The treatment also inhibits bacterial growth and extends the life of your sleeping bag. UltraDry Down treatment is an environmentally friendly application.