Yes, most roto-molded coolers will float. Not only do the thick polyurethane walls provide natural flotation properties, many of these coolers are also airtight and waterproof. This combination of properties adds to the polyurethane’s own ability to float by trapping air in the main compartment and keeping water out.
If you will be using your cooler in a marine environment and are concerned about its ability to float, consult the manufacturer’s specific product information for specific instructions.
Of course, even the highest-quality cooler will sink if water is allowed to enter the main compartment. It is important to ensure that all valves, drains, and lids are closed and that latches are secured if there is any possibility the cooler will fall overboard.