Abstract: Webbed multiple sheets comprising two substantially parallel, substantially plane polymethylmethacrylate outer layers and at least one center layer between said outer layers, wherein said outer layers and said center layer are bonded together into one piece by webs and wherein said center layer or layers comprise a thermoplastic material having increased tenacity, increased zero viscosity or a combination thereof in molten condition as compared with the material of said outer layers, thereby reducing sagging of said center layer or layers during extrusion.

Abstract: A method is disclosed for biaxially stretching a band of thermoplastic resin which comprises attenuating a band of unstretched resin, in a forming zone while the resin is in the thermoelastic condition, by passing the band between two surfaces spaced at a distance less than the thickness of said band of unstretched resin while permitting said band to expand in width, and then cooling said band to a temperature below the softening point of the resin while maintaining the dimensions of the attenuated and expanded band; apparatus for performing such a method is also disclosed.

Abstract: What is disclosed is a closure for closing the edge of a webbed structure having openings formed therein, said closure comprising a strip of flexible material having a plurality of projections formed thereon in a predetermined spaced relation selected to permit insertion of said projections into at least some of said openings, at least some of said projections including means for frictionally engaging the inner surfaces of the openings into which they are inserted to hold said strip on and against the edge of the webbed structure.