Polar bears are strong swimmers; they swim across bays or wide leads without hesitation. They can swim for several hours at a time over long distances. They've been tracked swimming continuously for 100 km (62 mi.).
A polar bear's front paws propel them through the water dog-paddle style. The hind feet and legs are held flat and are used as rudders.
A thick layer of fat, up to 11 cm (4.3 in.) thick, keeps the polar bear warm while swimming in cold water.
Polar bears can obtain a swimming speed of 10 kph (6.2 mph).
A polar bear's nostrils close when under water.
Polar bears make shallow dives when stalking prey, navigating ice floes, or searching for kelp.
Polar bears usually swim under water at depths of only about 3-4.5 m (9.8-14.8 ft.). They can remain submerged for more than one minute.
Maximum dive duration is unknown; however the longest polar bear dive observed to date lasted a total of 3 minutes and 10 seconds covering a distance of 45 to 50 m (148–164 ft.) without surfacing.
No one knows how deep a polar bear can dive. One researcher estimates that polar bears dive no deeper than 6 m (20 ft.).
Body temperature, which is normally 37°C (98.6°F), is maintained through a thick layer of fur, a tough hide, and an insulating fat layer (up to 11 cm or 4.5 in. thick). This excellent insulation keeps a polar bear warm even when air temperatures drop to -37°C (-34°F).
Polar bears are so well insulated they tend to overheat.
Polar bears move slowly and rest often to avoid overheating.
Excess heat is released from the body through areas where fur is absent or blood vessels are close to the skin. These areas include the muzzle, nose, ears, footpads, inner thighs, and shoulders.
Polar bears also swim to cool down on warm days or after physical activity.