All Spark sleeping bags are characterised by their ultra-light weight, minimal packing size and excellent thermal performance. The SpIV features vertical boxing compartments that are stitched throughout to provide extra moisture and reduce cold bridges. The expedition size provides extra space for additional layers of clothing. The vertical chambers in the chest area optimize the distribution of the down and prevent slipping. A full-sided zipper with two sliders allows easy access and variable ventilation. A zipper channel, a hood and a heat collar prevent heat loss. Ultra Dry DownUltraDry Down is a PFC-free water-repellant treatment applied to the down used in all Sea to Summit sleeping bags. UltraDry Down retains over 60 % more loft, absorbs 30 % less moisture and dries out 60 % faster when compared to untreated down – which means the down will insulate better even in damp conditions. The treatment also inhibits bacterial growth, making your bag last longer. UltraDry Down treatment is an environmentally friendly application.