To build the igloo, the builder takes a deep snowdrift of fine-grained, compact snow and cuts it into blocks with a snow knife, a swordlike instrument originally made of bone but now usually of metal. Each block is a rectangle measuring about 2 feet by 4 feet (60 cm by 120 cm) and 8 inches (20 cm) thick. After a first row of these blocks has been laid out in a circle on a flat stretch of snow, the top surfaces of the blocks are shaved off in a sloping angle to form the first rung of a spiral. Additional blocks are added to the spiral to draw it inward until the dome is completed except for a hole left at the top for ventilation. Joints and crevices are filled with loose snow. A clear piece of ice or seal intestine is inserted for a window. A narrow, semicylindrical passageway about 10 feet (3 m) long, with vaults for storing supplies, leads into the igloo. Drafts are kept from the main room by a sealskin flap hung over the exterior entrance to the passageway and by a low, semicircular retaining wall that is sometimes built out a few feet from the end of the tube. The major furnishings are a shallow saucer to burn seal blubber for heat and light and a low sleeping platform of snow covered with willow twigs topped by caribou furs.

The dimensions of igloos vary, but they generally accommodate only one family. An experienced Inuit can build a snow igloo in between one and two hours. Sod, stone, and wood have also been used to construct igloos.