They are usually treated first.
Remember the Tyvek rage for wings back in the mid-90's??
Tiers were driving around to construction sites to pick up discarded Tyvek sheets. LOL
I read that Italian tea bags are the best....back to the store Ed!
http://www.flytyingforum.com/index.php?showtopic=268
http://www.flytyingforum.com/index.php?showtopic=54639