Black Card alternative sizes

Quality Black Card in a choice of interesting sizes, A5 when folded will fit a C6 envelope or 79mm x 216mm envelope if folded lengthwise.  The  296 x 148mm when folded will make a square card to fit the 155mm (approximately 6") envelopes, whilst the 94 x 188mm when folded will make a square card to fit the 100mm (approximately 4") square envelopes.