Abstract: An expandable introducer sheath for use in interventional procedures. The expandable introducer sheath can be inserted into a treatment vessel in a first unexpanded configuration. The expandable introducer sheath can expand in diameter during insertion of a device through its main lumen and can then re-collapse down to its unexpanded diameter. The device comprises an inner heat-set folded layer and an outer elastomeric layer. The outer elastomeric layer provides a barrier between the inner folded layer and a vessel wall during unfolding of the inner folded layer to minimize the risk of vessel trauma.