Automatic thermosealer

It is provided a method of producing envelopes (13) from a roll (3a) of coated paper (3) for holding instruments (12) to be sterilised in an autoclave using a thermosealer (1), the method comprising the following steps: measuring the length of the instrument to be sterilised (12); feeding an amount of coated paper (3) adapted for said instrument to be sterilised (12); carrying out a first sealing and cutting operation on the coated paper (3) so as to produce the envelope (13) including an open side (14); introducing the instrument (12) into the envelope (13); inserting the envelope (13) at the open side (14) into a slit (15) present in the thermosealer (1); making the second sealing of the envelope (13) at the open side (14); wherein the coated paper (3) disposed in the thermosealer (1) is automatically retracted immediately after the first sealing and cutting operation has been carried out so that accomplishment of the second sealing is made possible without damaging the end portion (36) of the roll (3a).