Nobody buys a house without researching the neighborhood and inspecting the foundation, plumbing, and electrical. Yet many people drop serious money on a metal sofa bed without understanding what goes into a well-made piece of upholstered furniture.

　　The quality of the frame, suspension, cushioning, and upholstery are what separate a sofa that will last 10 to 20 years from one that will start to wobble or look dingy after only a few.

　　In addition to more than 80 hours we’ve spent researching for our sofa buying guide and coverage of the best online sofas, helped us understand the difference between an average-priced sofa (say, under $1,000) and a more splurge-worthy equivalent.

　　The frame

　　Everything begins with the frame. It’s an assertion we heard several times over when we asked experts and retailers where to begin when searching for a sofa designed to be used daily and to hopefully last for years. The type of wood used for the frame and how each piece is joined not only determines a sofa’s durability, but will also be reflected in its cost.

　　Slower-growing, denser hardwoods like alder, poplar, maple, teak, and walnut are more expensive, but are generally considered more suitable for durable furniture, and will typically outlast faster-growing and economical softwoods like pine and Douglas fir, doing a better job of holding staples, nails, glue, and joinery in place. (“Hard” and “soft” have nothing to do with the hardness of the wood, simply distinguishing coniferous evergreens (soft)from deciduous (hard) trees.)

　　The strongest and most expensive frames are constructed using the labor-intensive and traditional technique of mortise-and-tenon joinery, connecting pieces of wood with precisely routed tabs (tenons) that fit into holes (mortises). Only the best and more expensive sofas (like those from Modernica) are made this way and you’ll hardly ever find a mortise-and-tenon-constructed sofa for under $2,000.

　　More likely you’ll find mid-priced sofas constructed using a combination of glue, screws, dowels, and staples with the addition of corner blocks and extra pieces of wood screwed into place as an insurance policy against wobbling. Siegel recommends that you look for 1¾-inch staples for structural reinforcement, though warns that too many staples can be a sign of shoddy craftsmanship, weakening the strength of the frame by damaging the wood. Even skilled salespeople may not know the type of staples used in a particular sofa, though, and manufacturers may not reveal these specifics.

　　The suspension

　　If the wood frame is the skeleton of a sofa, the springs stretched across it operate as the seat’s tendons and ligaments, weathering structural stress and preventing the cushions from flattening. Cushions may give a sofa shape, but it’s actually the springs that primarily determine its comfort.

　　Sinuous springs are the most common suspension system in mid-tier sofas. They’re made with heavy-gauge steel wires bent into a continuous lineof vertical S-shaped coils. Horizontal metal tie rods reinforce the coils, inhibiting shifting and sagging, and are secured to the frame using padded clips and fasteners. I’ve personally owned two sofas for 14 years with a sinuous-springs system, and neither have shown any signs of sag or wear. They hit the sweet spot within the Venn diagram of comfort, affordability, and lasting durability.

　　Traditionalists extol the virtues of eight-way hand-tied springs. The time-consuming technique requires a furniture maker to strap and hand-knot individual hourglass-shaped coils with cord across the seat’s frame. When installed properly the hourglass springs supposedly ward off sagging and squeaking.

　　The cushioning

　　Beyond aesthetics, the subjective nature of cushions invites the widest (and most passionate) range of opinions when it comes to sofas. Some people love sinking into the upholstered embrace of a cushy-soft couch, others prefer a sofa with a firm feel and resilient shape. Identifying your preference will determine which of the following four cushion options you should consider:

　　Poly-wrapped foam: The majority of sofas manufactured today feature seat and back cushioning filled with layers of high-resiliency foam, a high-response material characterized by an open-cell structure, resulting in a supportive feel that dependably retains its shape over time (in contrast, a slow-response material like memory foam contours and deforms with use). A polyester wrap and a tight-weave down-proof ticking surround the foam center, resulting in a low-maintenance cushion that does not require fluffing.

　　Goose/duck down: You’ll find this naturally soft filling inside some of the most expensive sofas, filled either with 100 percent down (plush) or a down-blend encasing a foam core (slightly firmer) with a layer of down-proof ticking.Expert warns to check the down-to-feather ratio, so that you’re not paying for down when you’re getting mostly feathers, and recommends looking for cushions with channelled envelopes to keep down filling evenly dispersed. Even with sewn-in baffling, you’ll definitely need to rotate, flip, and fluff down-filled cushions regularly, as down has a tendency to flatten and clump with use. Just like a down bed pillow, 100 percent down will deform faster and require more fluffing. A 50-50 blend will likely be a little firmer and more affordable. Anyone allergic to feathers should avoid this option completely.

　　The upholstery

　　Never judge a book by its cover, and never pick a sofa solely by its fabric. That said, upholstery truly matters, as it’s what you’ll see and feel for years after purchase. If maintained with care, certain high-performance fabrics can last for over a decade. Both natural fibers and synthetics offer varying degrees of durability, with natural fibers generally revealing a richer depth of color, and synthetics exhibiting a smoother feel.

　　The legs

　　Years ago I made the mistake of purchasing a sofa outfitted with low, metal hairpin legs. They looked great in the showroom, which had impervious sealed cement floors. But they left my apartment’s original oak floors scraped like a 5-year-old’s knee after a skateboarding mishap. I was eventually forced to purchase carpet tiles to prevent further damage. Considering the material, diameter/surface area, and shape of sofa legs in relation to flooring ahead of purchase will prevent experiencing a similar “oh no” moment.

　　Sofa legs and feet are mostly made of wood, offering an opportunity to inspect a sofa manufacturer’s eye for grain and finish consistency. Check for uniformity in height and if the stain finish matches between feet and frame, and inspect each piece to confirm that it is securely fastened by getting down to the ground and giving each piece a pull, wiggle, and twist. Also ask if there are any uninstalled feet available for closer inspection. Avoid sofas with legs attached directly into the frame with screws—they’re susceptible to loosening over time under the duress of shifting bodies. Instead, look for legs and feet attached using thick threaded hanger bolts secured with T-nuts, which you can easily adjust or replace.

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