DetailsShasta Down Jacket III Size Chart The CIRQ Shasta Down Jacket III is named after the solitary imposing peak sitting at the southern end of the cascade range in California. Lightweight and packable, this is a multi-functional do everything insulated jacket. It's perfect for tackling mountain peaks when the weather system amplifies or relaxing by the campfire after the summit. It's made with a silky-smooth and down-proof fabric that takes your comfort to the next level without sacrificing function. This fabric works by keeping the warmth in and the cold out all while improving durability. The Shasta Down Jacket has room to layer over your favorite shirts and light sweaters while still being close fitting enough to layer under most technical outerwear.