Down feather jackets are stuffed with goose feathers, which are soft and warm in cold weather. They help trap warm air close to the body. However, these goose feathers can condense with time and also have a pointed quill that can poke through fabric and loose seams. Preventing the loss of valuable goose down is accomplished through good maintenance. Check the jacket repeatedly, sew up any tears and dry the jacket carefully to revive flattened down.
Look over your jacket for any rips, tears or loose seams. Sew them up with a needle and thread using tiny stitches. Stitch over seams in the jacket that appear to have large stitches that leak down.
Sew a second inner lining, using the jacket as a template. Use measuring tape to get all of the measurements exactly right. Mark them out on a piece of lining fabric and cut. Sew the inner lining pieces with right sides together. Fold any exposed edges under and stitch. Sew the second lining into the jacket with a machine top stitch or by hand with a whip stitch. Remember to use tiny stitches.
Push any feathers that poke through the fabric back inside. This may leave a small hole or stretched area in the fabric. Turn the jacket over and massage the hole through the inside of the fabric. This will help close up the hole in the fabric so that more feathers don't escape.
Put the jacket in the dryer on a low setting with a couple of tennis balls or knotted towels. The heat helps expand the feathers so they don't escape, and the tennis balls or towels will help fluff the feathers back up.