A staple cartridge is disclosed. The staple cartridge includes a cartridge body, a plurality of staples, and an implantable layer. The implantable layer includes an inner portion, an outer portion positioned at least partially around the inner portion, and a plurality of passages formed through the outer portion toward the inner portion. The implantable layer is porous. An implantable layer includes an outer portion including a plurality of fibers. A method of forming an implantable layer for use with a surgical stapler is also disclosed. The method includes forming at least one passage through an outer surface toward an inner portion of the implantable layer.
