An anvil-attachable layer and a retainer for aligning and attaching the layer to an anvil of a surgical stapler. Embodiments of the anvil-attachable layer can include one or more attachment features extending from the layer. A retainer can push the attachment features into a knife slot in the anvil so that the fit between the attachment features and the slot hold the anvil-attachable layer in place. Other embodiments of the anvil-attachable layer can include deployable attachment features formed in the layer. The deployable attachment features can be deployed from an undeployed position substantially in a plane defined by the layer to a deployed position extending out of the plane. In the deployed position, the deployable attachment features can extend into a slot in an anvil. A retainer can include features to push the deployable attachment features into the deployed position.
