SHEET FOR FORMING A PACKAGE

摘要

A sheet has a line of weakness 206 such as a perforation, cut or score line; and a layer 32 adjacent the line of weakness forms a valve 30 which opens in response to a pressure differential. The line of weakness can form the perimeter of an integral detatchable flap. The valve can extend up to or beyond this line of weakness. Ideally the sheet has multiple layers, a line of weakness 206 in one 200 being offset relative to a line of weakness 205 in another 202; resealable adhesive 203 can be provided between the lines so that the flap can be reclosed. There could be a tab extending from the flap to assist lifting and one of the layers can be a metal foil. The valve can be two or three time the thickness of the sheet the sheet can be used to form a package to contain a box or be contained in a box for tobacco.