Square envelopes are a particular style of announcement envelope with a deep square flap and double side seam construction most commonly used with baronial cards for informal mailings, social, and commercial announcements. Square envelopes are made with 28# white sulphite paper and come in various square sizes including 5x5 envelopes, 6x6 envelopes and more. Square invitation envelopes are perfect for that formal look when sending invitations or R.S.V.P. cards. The Supplies Shops also offers the panel cards that would fit these envelopes.