|By http://www.flickr.com/people/naturallight/ Leslie Philipp [CC BY 2.0], via Wikimedia Commons|
Eiders ducks use their down to line their nests so the Inuit harvest a small amount of down from the nests before the eggs hatch. The down is cleaned at the factory and sewn into the linings of parkas and duvets. Each nest yields about 70g of down. It doesn't sound like much but eiderdown is very expensive, selling for $330/kg.
To bad about the upside down postmark, but at least it was a good one. Here is it right side up, with a bit of Photoshop manipulation to bring it off the envelope.