A device comprises a spring and a sleeve. The spring is configured to form a closed loop. The spring is moveable between a coiled configuration when the spring is collapsed and an uncoiled configuration when the spring is expanded. The spring defines a circumference while in the uncoiled configuration....http://www.google.es/patents/US7335080?utm_source=gb-gplus-sharePatente US7335080 - Collapsible flotation device
