One of the most important furniture investments people make is upholstery. Unfortunately, it is probably one of the least understood. We cannot count the number of times people have told us: "I am going to get the cheapest sofa I can buy, because the kids are just going to jump all over it."  This is a bad strategy. A better approach is to spend more. You get a well-constructed piece, which will stand up to all sorts of abuse including kids and last you a long time. FRAME. Look for one made of kiln-dried hardwood, such as oak or alder. The process of kiln-drying makes the wood more stable and less likely to swell or warp. How the frame is constructed is as important as the materials from which it's made. High-quality frames are screwed and glued at all the joints, to doubly protect against any thing coming apart. Sofa corners should be reinforced with blocks connected with double dowels or staples and screws.   RULE OF THUMB. Lift sofa up before buying. If it is well-made, it will be heavy. A light sofa is not one that will last you long. SPRINGS. There are basically three types: 8-WAY TIED - a spring that moves in all directions, giving the seat the most flexibility and the most  comfortable sit. Unfortunately, this process can only be done by hand, and consequently drives up the cost of your piece of furniture. Most sofas and chairs from large manufacturers do not feature eight-way springs. DROP-IN COIL - It comprises a pre-made armature of coils connected to one another by metal clips, which is inserted into the sofa base. The armature is then fastened to the frame, typically at the corners. Drop-in systems are equally durable as hand-tied systems and may reduce a sofa's price. SINUOUS - It's made by attaching S-shaped or zigzagged steel wires to the frame and stretching them from front to back or top to bottom. It lacks the localized response of a coil system but gives a firm ride that some people prefer, and has less potential for sagging over time. Sometimes zigzag suspension is employed for aesthetic reasons when a designer wants a tight, clean-lined seat. CUSHIONS. Most cushions are made of a Dacron foam core that is then wrapped in either down, more foam or a hypo-allergenic down substitute. Seat cushions should not be 100% down; the cushions will go flat as the down breaks down and it will look like a mess. Foam core gives structure to a cushion and allows it to hold it's shape. Remember that a down cushion will always need fluffing. Only an all-foam cushion will hold a perfect shape but the sit will not be as luxurious. UPHOLSTERY.  More than any other element of your sofa, the upholstery you choose will affect the price you pay. So when selecting a fabric, you'll want to balance considerations of budget, aesthetics, and the material's durability. Fabrics are also coded for how they can be spot-cleaned: W is for water-based agents; S for chemical solvents; WS for either water or solvent; and X means brush-clean only. Unless your sofa is only for show, stay away from X!