U-type enclosure

A paper, polyester or hybrid (polyester front; cotton paper, paper or cardboard back) enclosure with three edges glued or sealed. It limits the risk of accidental sliding out of  a stored object.   

Please note: this construction cannot be used to store large and supple objects (such as plans, maps, graphic art). In case of such objects an I-type enclosure or an L-type enclosure are a safer solution - they are easier to slide objects into.