These envelopes are made of bright white paper. However it is not very weighty nor are they cut cleanly. There are cuts that are jagged not straight. For the price it seems the paper could be a little heavier and the cuts on all the edges should be straight and even. I would expect this quality from a discount store - not Staples.
The #9 gummed envelopes are the correct size for our use: Return envelopes stuffed inside a #10 mailing. However the gummed edges are already sticking (perhaps due to moisture). This occurred almost immediately upon use. Maybe a bad batch! I suggest you make them will peel seals.