Abstract: An air interface of a flexible and airtight material includes a first ring and a second ring (both adjustable in size), a first ring holder to removably hold the first ring, a second ring holder to removably hold the second ring, a cord holder, and a cord with a lock-and-release mechanism to adjust its effective length. The first and second ring holder and the cord holder create a saddle between the first ring and the second ring, and an extension between the second ring and the cord. The extension can be wrapped over the saddle and back up to create a pocket. A flexible duct can be wrapped around the second ring. The end of the flexible duct can be thickened or tightened and inserted into the pocket. The flexible duct is trapped in (or released from) the pocket by adjusting the cord's effective length.