5 Star C5 Window Pocket Envelope Self Seal 90gsm 229x162mm White (Pack of 500) M900175 Star white C5 envelopes. These envelopes have a blue opaque interior for security and are made from lightweight 90gsm paper, making them perfect for everyday use. They also feature a window which allows you to clearly display the address of your correspondent. C5 size 229x162mm Made from lightweight 90gsm paper Window size of 100x40mm Window position 62mm in from LHS, 25mm up Self seal closure contains a strip of gum on each flap which when pressed