You get hot on the climbs, and cold on the descents. It's one of life's certainties, along with death and taxes.
Chromag made the Col to keep the wind out and the warmth in, with the added benefit of the Stash pocket to pack it into and strap to your frame when you're up to temp.
The Col packs snuggly into its pocket, and can be securely attached to your bars, saddle rails, or frame with the attached Velcro strap.