Our regular white non-window envelopes are made from 24# white wove paper. This is the same great quality you would find at your local print shop. Our envelopes work great in mailing equipment such as inserters. We carry three sizes of this standard business envelope. The #10 envelope is the standard letter size envelope used for business letters, invoices and marketing pieces. The #9 envelopes fits nicely into our #10 Envelope. These are used for reply mostly. You can insert a #9 envelope into the #10 envelope so your customers or can send back checks or responses. The U.S. Postal Service can set you up with the proper bar codes to send us so we can print pre-paid reply envelopes. And finally our 6-3/4 envelope. This envelope can be used like the #9 envelope, it's just smaller. See product details for actual sizes. The 6-3/4 envelope is popular as a donation envelope or a church offering envelope.