C5 envelopes are used for correspondence that allows a standard A4 sheet to be folded in half, so for less formal mail. C5 envelopes measure 162 × 229 mm - allowing you to pack an A5-size sheet of A4 folded in half comfortably. Self-adhesive tapes are often used on the closure flaps on the shorter side, allowing the mail item to be sealed quickly, permanently and tightly. C5 envelopes are available in white and brown, as well as with a foil window.