Heat sealing service for formed blisters, closing each cavity with aluminium foil, laminated film or printed foil as the lidding. A stainless-steel sealing line feeds foil over clear formed blister webs, producing finished trays with rounded rectangular pockets on a flat backing. The seal is uniform and tamper-evident, keeping out moisture, dust and contamination, and the line runs at speed for bulk orders, with printed foil supplied to the buyer's own design.