Option 1 medium Upholstered furniture has a frame, izgotavleny of wood. For supporting part (on which you sit) used a strong beam cross-section 40×60 and more. It is best if you use solid hardwood wood (oak, birch, beech). Nevertheless, the vast majority of producers use pine (2 times cheaper). Not always – the highest quality and very often – not that section that you want. With imported furniture – simple.
Manufacturer necessarily indicate that information in its catalog, as application framework for the more expensive hardwood (not coniferous) wood is a competitive advantage, and be silent about it would be just silly. Sides are made from the couch glued together sticks of wood (laminated veneer lumber), but can in another way: Wooden sheathing, not fixed bars cardboard, beat them (to keep) nails. The second option, Naturally, less expensive, but worse. For non-structural parts of the carcass can be used conifer wood, because these parts are not exposed to extreme loads. How and what made frame, you never know, except that 'Will open' sofa.
Option 2 is optimal. Upholstered furniture with a frame of plywood. Plywood is more expensive than natural wood and are much more expensive than particleboard. Depending on the quality and thickness, the price of plywood is 10 – $ 20 per m2, which is why furniture significantly more expensive. Plywood – a light and strong material, relatively 'clean'. In the production of plywood sheets peeled veneers glued together with alternating transverse fibers, and equity. This gives plywood maximum strength, higher than the wooden beam of similar cross-section.