Premium latex and viscoelastic ''memory foam'' mattresses look and feel luxurious, but you can also put one together from components that matches the name brands in quality, for hundreds of dollars less.

FOAM FACTS

Viscoelastic foam Known as ''memory foam.'' A special type of polyurethane foam developed by NASA to cushion astronauts in flight. Heat-sensitive, it provides support and relieves pressure by conforming to the body’s shape.

Latex foam Derived from the rubber tree, it is naturally resilient and supportive. It lasts much longer than other foams, and is resistant to dust mites, mold, mildew, and bacteria. Talalay latex does not trigger latex allergies.

Polyurethane foam The most common kind of foam in traditional mattresses. Its chief attribute is its low cost, but high-resiliency polyurethane foam can last 10 years or so, depending on the type.

WHAT TO LOOK FOR

Density In high-density foam, cells are typically packed more tightly together, so foam withstands repeated compressions better. Look for foam of at least 3 lb. per cubic foot. Talalay latex foam is 5 lb. per cubic foot and is said to last 20 years or more.

Firmness Unrelated to density. Low-density foam may feel firm at first, but will break down relatively quickly. Firmness is measured in ''indentation load deflection.'' For firm support, try foam with an ILD of 30 or higher. Medium firmness is 25 to 29 ILD.

Brand Talalay latex foam and Tempur-pedic and Sensus memory foam are respected brands.