Light weight expansible mailing envelope

Claim 1

A lightweight expansible envelope for overseas mailing of generally bulky materials and documents especially via airmail comprising: a one-piece blank including generally rectangular front and back panels, sidewalls interconnecting the respective opposite lateral edges of the front and back panels and including inwardly folded gusset sections defined by triple score lines and lying flatly between said front and back panels when the envelope is in flat disposition, a bottom interconnecting the adjacent lower edges of said front and back panels including gusset panels defined by triple score lines and adapted to be opened into boxlike configuration with respect to said front and back panel when the envelope is expanded, a substantially rectangular sealing flap hingedly connected to the upper edge of said front panel and adapted to define a closure for the open end of the envelope, corner closure extensions of generally rectangular configuration hinged to the lateral edges of said sealing flap and to the upper edge of each of said side gusset sections, said corner closure extensions including free edges respectively intersecting with the lateral edges of said sealing flap and the upper edge of said back panel to define a plurality of 90* intersections adjacent the open end of the envelope, and a concave radiused filet included within each 90* intersection thereby providing resistance to tearing at the open end of the envelope adjacent intersecting planes which are not coextensive in configuration.