A short history of chairs
The positions in which people have sat have varied from period to period, culture to culture and continent to continent. In some places sitting cross-legged has been the most common posture, in others kneeling has been the norm, and in yet others squatting is considered natural and comfortable.
With such a variety of sitting positions to choose from, why have people in the Western world chosen our traditional sitting posture as the pattern for virtually all chair design?
The answer is simple – throughout the ages, society in general has imitated the higher social classes, and the modern chair evolved from the thrones used by royalty.
Following the Industrial Revolution, more and more work was carried out while sitting, and by the twentieth century, homes in the West were filled with chairs.

Structures
The primary function of a chair is to hold up and support the human body when sitting.
Designers must make sure that chairs are not only comfortable to sit on but that they can support the different weights of all their users and that they stand up to wear and tear. When it sits down the human body exerts a force that moves the chair. The chair will not buckle or break under this force if its construction has been carefully planned, even if someone tips back on it.
Designers constantly explore different ways of approaching the construction of chairs and some are more successful than others. The suitability or otherwise of different materials can have a drastic effect on the success of a chair design.

Environmental Design
Sustainability
Designers can deal with concerns for the environment in several ways. Making sure that a product has durability is important from an ecological perspective. Peter Opsvik designed the Tripp Trapp Chair with this in mind: ‘If materials are handled with loving care during the development and processing stages, the chances of a product being taken care of and lasting for a long time are much greater.’ The choice of materials is another important aspect of sustainability. 
Manufacturers Totem Italia are committed to sustainable design in a much broader context than recyclable materials. ‘We choose to use eco-friendly materials because of the low impact they have on the environment as they are retrieved and processed. This is also part of our commitment to upholding ethical production processes for human and natural resources, as well as safe-guarding the health of the artisans who make our products and the customers who use them.’

Using new materials
The designer Jane Atfield used recycled plastic sheet for her child’s chair, the RCP2. Small pieces of waste plastic detergent bottles were heated and then compressed to form a sheet of the material. In some places the original printed text from the bottles can be seen, and changes in the colour of the detergent bottles result in instant changes in the colour of the material. The chair has been produced by manufacturers Made of Waste since 1992.

Case study: Sedia Misura
This chair by Totem Italia demonstrates their commitment to using natural, economical materials. 
They use birch/beech plywood and solid wood; each structure makes best use of the flexibility and strength of the material to produce extremely lightweight yet solid, stable furniture. Clever construction means there is no need to use glues: the plywood pieces are precision-cut by laser to ensure a proper fit and held together in constant tension. The seat of the Sedia Misura is held in place by a rubber band and the surfaces can be coloured or finished with natural oil.
Totem’s furniture range is sold in kits, which makes it easy to transport and store. Each kit includes the chair parts, any accessories, assembly instructions and oil for finishing.
No metal or adhesive material is used in the construction of any of the products and no tools are required to assemble any of the items.

Case study: Wiggle Side Chair
In the 1960s a trend for cheap and lightweight materials resulted in the development of cardboard as a material for furniture design. Although this was more ecologically sound than plastic it did not have its durability. 
In 1972 North American architect Frank O. Gehry developed a cardboard material that he named ‘Edge Board’. The material was constructed by gluing layers of corrugated cardboard in alternate directions, a similar construction to plywood, and it was suitable for creating both sculptures and furniture.
Although the furniture range was immediately popular Gehry discontinued production because he wanted to concentrate on architecture. The chair is manufactured today by Vitra AG.

Case study: Louis 20
This armchair by Philippe Starck can be used both inside and outside for domestic or public seating and is recyclable. 
The springy back section and the curvy hollow front legs are manufactured from one piece of blown polypropylene; the arm rests and back legs from over 99% pure aluminium. It is held together with a minimum number of screws and can be disassembled very quickly by unscrewing the back legs from the body, thus making it easy to recycle the two materials separately.
The aluminium frame is joined to the body by a plate that enables the chair to be tilted on the back legs without causing damage.