Ever wonder why they are called Manilla Folders?

The Manila folder was invented in 1930 in the Philippines. It is made of thick, durable Manila paper and sized so that full sheets of printer paper can fit inside without folding. As with the Manila envelope, it is traditionally buff in color. It often has a mechanism on the closing flap that allows it to be opened without damaging the envelope so that it can be reused. In a more general sense, envelopes made of brown, unbleached paper, used for cheapness, are described as Manila envelopes.