Dust-proof reinforcing sheet material to be applied over handling opening-formed on wall of box

A dust-proof reinforcing sheet material to be applied over and around an opening provided through a wall of a box for handling the box, said sheet material comprising a base sheet having a row of through-holes punched out to be arranged equidistant apart, an adhesive layer applied on one side of said base sheet, and an elastic film applied on the other side of said base sheet to extend over said through-holes, said elastic film being stretchable to have an area of five times or more of the orignial surface area thereof so that the film is stretched to permit easy insertion of fingers of a handler when the handler desires to handle the box, and said elastic film being transparent or translucent to allow light rays to transmit therethrough so that the position of the sheet material may be sensed by photo-sensor means and the sheet material is cut at a precise position.