Watch bands can be provided with an ability to dynamically adjust the fit of a watch against a wrist of a user. One or more of a variety of tensioning elements can be provided with a shape memory polymer that responds to a stimulus to adjust a fit of the band. Such stimulus can be from user or actively applied by the watch. The shape memory polymer can be a composite material that provides high durability under cyclic stretching and high speed response of shape recovering while avoiding a drastic moduli drop by shape recovering.