If your puffer jacket has been squashed and flattened, there are several methods you can try to restore its fluffiness:

1. Hang it up: Hang your puffer jacket on a hanger in a well-ventilated area. Gravity will help the jacket expand and regain its shape. Be sure to avoid hanging it in direct sunlight, as this can cause the fabric to fade.
2. Tumble dry with tennis balls: Place your puffer jacket in a dryer with a few clean tennis balls. The tennis balls will bounce around and help to fluff up the down filling. Use a low heat setting and check on the jacket frequently to avoid overheating.