DetailsJack Wolfskin Men's Size Chart If light and warm is what you’re after, the JWP Down is the jacket for you. It has a very small packed size and weighs next to nothing, so it’s ideal for active travel and spur-of-the-moment adventures. The jacket has a high performance RDS-certified duck down fill. A windproof STORMLOCK shell provides double protection: it shuts out the wind and shrugs off light showers. The JWP Down is also very breathable, which makes it ideal for energetic outdoor sports.