If a jacket is "down filled" it is filled with down. Down is the name for the delicate, lightweight feathers from a bird's belly, usually duck or goose.
It's a jacket used during snow. It basically is a coat filled with feathers that traps the air to create insulation.
Rab jackets would generally be worn in the fall and winter months. Rab jackets are primarily made for alpine skiing and other winter sports. They are usually down filled.
it is filled with all that radiation and keeps the warmth in it
Moncler Jackets are worth buying given their feather down, and design.
Down jackets are so-called because they contain down, the fluffy feathers found in the undercoat of a duck or goose. Some cheaper down jackets also contain small feathers.
Quilted jackets are typically made from scrap pieces of cotton fabric that is sewn together and then filled with quilt batting or cotton batting. The colors can vary greatly.
Eastern Mountain Sports, Eddie Bauer, REI and Cabelas sell men's down jackets. Each of these retailers also has an online store where you can purchase the jackets.
In what context? I would think it means you can't wear jeans or jackets.
Letterman jacket
the chap with a spanner down his pants
There are numerous retailers where one can purchase Down jackets for men online. They can be purchased online from 'Go Outdoor', 'Amazon' and 'Dick's Sporting Goods'.