a plus for the Tyvek envelopes...if you're into painting, art quilts, etc, tyvek can be painted, stitched (without tearing out), and when it's heated with a heat gun it bubbles up and changes shapes....I've used it in a couple of art quilts and love to play with it. If you receive a tyvek envelope in the mail, hang onto it and play with it some day or find a person who does art quilts and give it to her/him.