A membrane for use in connection with a closed system transfer device has a body with a proximal portion opposite a distal portion along a central axis and a skirt extending radially outward from the distal end such that a lip is formed at a transition between the proximal portion and the distal portion. The membrane further has at least one well recessed in a proximal direction from a distal end of the distal portion, thereby forming a channel within the distal portion having an open first end, a closed bottom end, and a pair of sidewalls extending between the first end and the second end. At least one slit extends through at least a portion of the body in a direction of a plane aligned along or parallel to the central axis.
