Gusseted plastic bag

Claim 1

AN OPEN-MOUTHED BAG OF PLASTIC SHEET MATERIAL COMPRISING, IN ITS FLATTENED FORM: A FRONT PANEL AND A BACK PANEL; TWO SIDE GUSSET PANELS FOLDED BETWEEN AND JOINED TO SAID FRONT AND BACK PANELS, EACH SIDE GUSSET PANEL FORMING A FOLD WITH A RE-ENTRANT ANGLE; AT EACH SIDE OF THE BAG, IN A POSITION TOWARDS THE MOUTH THEREOF, A SEAL JOINING TOGETHER THE FRONT AND BACK PANELS AND THE FOLDED SIDE GUSSET PANEL THEREBETWEEN, SAID SEAL EXTENDING INWARDS BEYOND THE RE-ENTRANT ANGLE OF THE SIDE GUSSET PANEL; AND AN OPEN-MOUTH PORTION FORMED BY ONLY PARTS OF SAID FRONT AND BACK PANELS PROJECTING BEYOND A LINE JOINING THE POINTS OF INTERSECTION OF SAID SEALS WITH THE RE-ENTRANT ANGLES OF THE GUSSET PANELS, SAID OPEN-MOUTH PORTION HAVING ONLY A CONSTANT NUMBER OF LAYERS OF MATERIAL THROUGHOUT ITS ENTIRE WIDTH, WHEREBY THE OPEN-MOUTH PORTION MAY BE COMPLETELY SEALED IN A SINGLE STEP AND WITHOUT INTERFERENCE FROM A CHANGING NUMBER OF LAYERS OF MATERIAL ACROSS THE WIDTH OF THE BAG.