Before describing what makes them different, let's discuss quickly what makes them similar. They are both types of Self Seal envelopes, that, unlike traditional gummed envelopes, do NOT need to be moistened to seal. SIMPLE SEAL: A simple seal envelope is a commercial envelope that has "Flip-n-Stick" flaps that make it quick and easy to seal your envelopes. This envelope has two latex surfaces that seal on contact. You simply turn up the bottom flap, turn down the top flat, and on contact.... the envelope seals. PEEL & SEAL: With a peel-and-seal envelope, you simply peel off a paper strip and press for a permanent seal.