apparatus and process for continuously and repetitively producing grocery sacks from a thermoplastic web at high speed , including particularly a folding operation involving applying grasping action to bag blanks formed from a heat sealed gusseted flattened tubular web of , e . g ., high density polyethylene at the upper and lower portions thereof , respectively , causing said portions to be forwarded at differential longitudinal speeds whereby a rough folded bag bottom is formed . preferably , the web is flexed as by introduction of air to the bag blank or sack to release the respective web faces and facilitate folding . a complete apparatus includes sealing , cutting , folding and pressing means and may incorporate printing and like ancillary features .