These are level 6 extreme cold weather, wet weather outer jackets. These jackets protect the wearer from the elements with a Gore-tex lining and help protect the user when using the ECWCS system to 14 degrees below Fahrenheit.
When trying to stay warm in cold weather its important to wear layers. You should have a polyester base layer, then a fleece or grid thermal (waffle thermal) and then on top of it all the Gore-tex waterproof shell. The waterproof shell is critical because if you get wet in extreme cold weather it only takes minutes for hypothermia to set in.
These Gore-tex jackets are a thin water proof layer that is meant to be worn with multiple layers of thermals underneath and for that reason they run 1-2 sizes large.