A staple cartridge for stapling the tissue of a patient is disclosed. The staple cartridge comprises a cartridge body, a plurality of staples, and a compressible tissue thickness compensator configured to adapt in thickness in response to the thickness of the tissue and adaptively apply different pressures to the tissue based on the thickness of the tissue captured within the staples. The compressible tissue thickness compensator comprises a plurality of fibers comprising a first matrix oriented in a first direction and a second matrix oriented in a second direction that is different than the first direction. A network of interstices is defined intermediate and among the first matrix and the second matrix. The network of interstices comprises a plurality of cavities that promote tissue and cellular ingrowth between the first and second matrices of fibers.