A staple cartridge comprising a cartridge deck, a longitudinal slot defined within the staple cartridge, staple cavities defined in the deck, and a tissue thickness compensator is disclosed. The tissue thickness compensator comprises lumens. Each of the lumens comprise a cross-section and are formed by a tubular element. The lumens are laterally-oriented and spaced on the cartridge deck along the longitudinal axis of the staple cartridge. Each lumen extends across the width of the staple cartridge such that each lumen overlaps a plurality of the staple cavities and the longitudinal slot. The lumens are configured to collapse when pressure is applied to the lumens during a firing motion.