Females can continue to breed until 20 years of age. At the start of the Arctic winter when the sun appears above the horizon, for a short period each day, the female polar bear starts to look for a place where she can give birth to her cubs. She seeks out a place sheltered by a valley, slope or cliff where winds have already piled the snow into drifts. Using her big and strong feet and claws she digs a tunnel into a sloping edge of snow. At the end of it she shapes a comfortable chamber packing and stamping down the snow.
Most dens are oval shape, six to nine feet long and about six feet in height and width.
Females give birth to one to three cubs, usually two. Cubs weigh only about 25 ounces and can fit into the palm of your hand. The young leave the den with their mother at about four months but remain with her for another year or so. Polar bears are fully grown at around five or six years of age. An adult male polar bear may measure more than nine feet in length and weigh over 2000 pounds.