If you count every gram but still value a restful sleep, the Spark is likely the right sleeping bag for you. The RDS-certified goose down filling, treated with a PFC-free Ultra-Dry down process and with a fill power of 850+, provides excellent insulation, supported by the technical hood and zipper cover. For comfort, there is a highly breathable inner material made of 10-denier nylon, while the 10D outer material features a PFC-free DWR coating, along with a highly water-repellent hood and footbox to keep out wind and condensation. The full-length zipper of the Spark 7C allows couples to connect it with another sleeping bag of the same model for added convenience and warmth efficiency.