Though important in building is garden use is rather limited but can if used carefully can be very effective. The term metal encompasses a vast range of material, many used since ancient times, and the suitability of a particular one will depend on the individual use planned.
This material combines concrete and steel to create a material with excellent compressive and tensile strength. This provides the potential to provide some very graceful and elegant structures but the complex nature of the material means is design and specification requires specialist expert knowledge.
Concrete reinforcing should not be confused with crack control in concrete, by weldmesh or polypropylene fibres, which serves a very different purpose.
Traditional plastic has not been used a great deal in garden construction but the vast range of different forms of plastics means it has great potential. It has the advantage that it is very rot resistant, can be moulded (and some can be machined), pre-coloured and even some is made from recycled materials means it is beginning to be used for more than pond liners and roofing sheets.
Used for hundreds of years, recent developments in glass technology means this is a material with great future potential.
Traditionally these have been used to make raised peat beds, but have they have fallen out of favour in recent years as a result of the environmental concerns around peat harvesting and use.