a volume of material having a first formation wherein the volume is substantially undivided by the material, and a second formation wherein the volume is substantially divided by the material, said first formation being shaped so as to enclose a user's torso and arms together in one compartment, said second formation being divided so as to form compartments suitable for separately enclosing each of the user's arms;

a transforming fastener coupled to the volume of material, said transforming fastener comprising:

a plurality of tracks, each track comprising a pair of matable rows; and

a slider slidably coupled to the rows, the slider transforming said volume of material, when sliding along said rows, between said first and second formations by fastening one of the pair of rows while unfastening another of the pair of rows.