A method for changing the spring rate of a tissue thickness compensator for use with a surgical instrument, said method comprising the steps of: obtaining a biocompatible polymer comprising a glass transition temperature and a melting temperature; dissolving said biocompatible polymer in a solvent to produce a solution; and lyophilizing said solution to obtain a tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) having a thickness and comprising a tissue-contacting surface and a deck-contacting surface, wherein said tissue-contacting surface and said deck-contacting surface are opposite one another and separated by said thickness, wherein said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) is compressible in the thickness direction so as to compensate for the thickness of tissue captured within staples deployed from a surgical staple cartridge and comprises a first spring rate, wherein said tissue thickness compensator is at least partially comprised of a material having a glass transition temperature and a melting temperature; heating said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to a temperature higher than said glass transition temperature and lower than said melting temperature; deforming said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to change said first spring rate to a second spring rate, wherein said second spring rate is different than said first spring rate so as to change the pressure exerted by the tissue thickness compensator against tissue captured within a staple; allowing said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to cool below said glass transition temperature; and releasing said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200). obtaining a biocompatible polymer comprising a glass transition temperature and a melting temperature; dissolving said biocompatible polymer in a solvent to produce a solution; and lyophilizing said solution to obtain a tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) having a thickness and comprising a tissue-contacting surface and a deck-contacting surface, wherein said tissue-contacting surface and said deck-contacting surface are opposite one another and separated by said thickness, wherein said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) is compressible in the thickness direction so as to compensate for the thickness of tissue captured within staples deployed from a surgical staple cartridge and comprises a first spring rate, wherein said tissue thickness compensator is at least partially comprised of a material having a glass transition temperature and a melting temperature; heating said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to a temperature higher than said glass transition temperature and lower than said melting temperature; deforming said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to change said first spring rate to a second spring rate, wherein said second spring rate is different than said first spring rate so as to change the pressure exerted by the tissue thickness compensator against tissue captured within a staple; allowing said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200) to cool below said glass transition temperature; and releasing said tissue thickness compensator (1104, 1120, 1140, 1150, 1170, 1190, 1200).