From Unitrade, these stock sheets are made of heavy 8-1/2 x 11″ manila stock. The sheets come with 12 pockets, with reinforced tape on the sides. Available in packages of 10 or 100. Manila sheets are also available with 4 pockets, for blocks. The pockets are single-sided.
Sorry, but the regular 12 pockets are currently on backorder with the manufacturer with no ETA.