For visibility when swimming, as additional buoyancy 

For taking a lap around the lake, training for your next triathlon, or open water swimming in the ocean. The inflatable swimming buoy offers increased safety, with visibility and buoyancy close at hand when you need it.

Simply fasten the belt around your hips, blow up the air chamber using the mouth valve, and pull the buoy behind you as you swim. The buoy creates almost no resistance in the water.

The Swim Buoy also enables you to store useful items in a separate compartment from the air chamber so they are easily accessible at all times.