Sofa construction can vary significantly with the use of different materials and methods of construction for the frame. Generally the frames are made with solid wood and the best furniture is made from hardwood such as oak, birch or alder. Using hardwood, particularly for the frame construction, lessens the chances for joints to loosen over time thereby increasing the life span of the sofa. Quite often plywood is used as it is a laminate material where thin layers of wood are sandwiched together using glue, with the end result being a very strong material. Plywood is generally used for the panels of sofa construction. Joints can be reinforced using gluing, screws and staples and the addition of re-enforced corners.
Whilst it is ideal to have a sofa made from expensive hardwood, most reasonable quality sofas have relatively well constructed frames. The softer parts such as the base upholstery and cushions are the main areas which take the majority of the wear and tear and it is less common to find a creaky sofa nowadays, unless you are buying at absolutely the bottom of the range.