Consumer lending makes up the bulk of North American bank lending, and of this, residential mortgages make up by far the largest share. Mortgages are used to buy residences and the homes themselves are often the security that collateralizes the loan. Mortgages are typically written for 30 year repayment periods and interest rates may be fixed, adjustable, or variable. Although a variety of more exotic mortgage products were offered during the U.S. housing bubble of the 2000s, many of the riskier products, including "pick-a-payment" mortgages and negative amortization loans, are much less common now.