B-10 Business Envelopes are also called #10s.  If you want an elegant way to make your correspondence stick out in the mail, this pack of standard, B-10 business envelopes is the way to go.

They come with four mailing labels and the envelopes are adorned with double-sided adhesive tape on the back, which make them easy to seal.  They are packaged in a transparent box. 

These business Cloth Envelopes can be mailed in the US with a first class self-adhesive stamp.

They are standard B-10 size: 4.125"x9.5"

They are perfect for official documents that you want to stand out in the mail and are also great for gifting money to relatives.