A coating 150 is applied to a substrate 140 using a flexographic 100 technique. The coating is dried to remove water. The coating is volumetrically expanded by means of heat and/or radiation. The preferred coating technique involves pan roller, transfer cylinder 110 and plate cylinder 120 with transfer pads in a pattern. An adhesive is preferably applied to the outer edge prior to the coating, enabling substrates to be combined. Preferably the substrate 140 is paper, and the coating 150 comprises polymeric emulsion containing microspheres which expand ≥ 100% upon infrared (IR) heating. The coated substrate is formed into padded envelopes.
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