Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature and skeleton by highly organized, fan-shaped networks of tendons and ligaments. It can comprise up to 50% of the body mass of some marine mammals during some points in their lives and can range from a couple of inches thick in dolphins and smaller whales, to more than a foot thick in some bigger whales, such as Right and Bowhead whales. However, this is not indictive of larger whales' ability to retain heat better, as the thickness of a whale's blubber does not significantly affect heat loss. More indictive of a whale's ability to retain heat is the water and lipid concentration in blubber, as water reduces heat retaining capacities, and lipid increases them.
Blubber is, however, different from other forms of adipose tissue in its extra thickness, which allows it to serve as an efficient thermal insulator, making blubber essential for thermoregulation. Blubber is also more vascularized, or rich in blood vessels, than other adipose tissue.
Blubber has advantages over fur (as in Sea Otters) in the respect that although fur can retain heat by holding pockets of air, the air pockets will be expelled under pressure (while diving). Blubber, however, does not compress under pressure. It is effective enough that some whales can dwell in temperatures as low as -40 degrees Fahrenheit. While diving in cold water, blood vessels covering the blubber constrict and decrease blood flow, thus increasing blubber's efficiency as an insulator.
Blubber can also aid in buoyancy, and acts to streamline the body because the highly organized, complex collagenous network supports the non-circular cross sections characteristic of cetaceans.
Research into the thermal conductivity of the common bottlenose dolphin's blubber reveals that its thickness varies greatly amongst individuals. However, blubber from emaciated dolphins is much worse of an insulator than that of non-pregnant adults, which in turn have a higher heat conductivity than blubber from pregnant females and pre-adults.
One of the major reasons for the whaling trade was the collection of whale blubber. This was rendered down into oil in try pots or later, in vats on factory ships. The oil could be then used in the manufacture of soap, leather, and cosmetics. Whale oil was also used in candles as wax, and in oil lamps as fuel.
Blue whales can yield blubber harvests up to 50 tons.
Recent studies suggest that blubber contains naturally occurring PCB, which are cancer causing and damage the human nervous, immune and reproductive systems. . It is not known where the source of this PCB is. Since toothed whales typically place high on the food chain, they are bound to consume large amounts of industrial pollutants. Even baleen whales, by merit of the huge amount of food they consume, are bound to have toxic chemicals stored in their bodies. Recent studies have found high levels of mercury in the blubber of seals of the Canadian Arctic.