A surgical instrument for the removal of biological material from a patient. The surgical instrument includes a specimen retrieval bag having a flexible wall and a closed end and an open end, wherein the open end is for receiving biological materials. The instrument includes a noose adjacent to the open end, wherein the noose constricts the open end to substantially close the open end. The bag includes a row of alternating flexible and stiff areas on its wall adjacent to and about a periphery of the open end, whereby when the open end is noosed, the flexible areas buckle before the stiff areas.