I got these for my bookkeeper and they work well. These are not thick envelopes, but certainly do the job. Also, they are not self-sticky - you have to seal them the old-fashioned way by wetting the dry adhesive on the flap to seal, but seals well. The windows work well with our business checks that are printed by our printer. The standard-size business checks fit perfectly in the number 9 size. It's exactly what we need and the price was reasonable.