Chairs can be made from wood, metal, or other strong materials, like stone or acrylic. In some cases, multiple materials are used to construct a chair; for example, the legs and frame may be made from metal and the seat and back may be made from plastic. Chairs may have hard surfaces of wood, metal, plastic, or other materials, or some or all of these hard surfaces may be covered with upholstery and/or padding.
The design may be made of porous materials, or be drilled with holes for decoration; a low back or gaps can provide ventilation. The back may extend above the height of the occupant’s head, which can optionally contain a headrest. Chairs can also be made from more creative materials, such as recycled materials like cutlery and wooden play bricks, pencils, plumbing tubes, rope, corrugated cardboard, and PVC pipe.
Design and ergonomics
Chair design considers intended usage, ergonomics (how comfortable it is for the occupant), as well as non-ergonomic functional requirements such as size, stacking ability, folding ability, weight, durability, stain resistance, and artistic design. Intended usage determines the desired seating position. “Task chairs,” or any chair intended for people to work at a desk or table, including dining chairs, can only recline very slightly; otherwise the occupant is too far away from the desk or table. Dental chairs are necessarily reclined. Easy chairs for watching television or movies are somewhere in between depending on the height of the screen.
Ergonomic design distributes the weight of the occupant to various parts of the body. A seat that is higher results in dangling feet and increased pressure on the underside of the knees (“popliteal fold”). It may also result in no weight on the feet which means more weight elsewhere. A lower seat may shift too much weight to the “seat bones” (“ischial tuberosities”).
A reclining seat and back will shift weight to the occupant’s back. This may be more comfortable for some in reducing weight on the seat area, but may be problematic for others who have bad backs. In general, if the occupant is supposed to sit for a long time, weight needs to be taken off the seat area and thus “easy” chairs intended for long periods of sitting are generally at least slightly reclined. However, reclining may not be suitable for chairs intended for work or eating at table.
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