I do not see any reason why this should apply to materials such as metals, paper and glass.

Her sculptures use materials such as glass, paper, metal and leather.

They may be made of any material such as nylon, metal or leather.

Different materials, such as paper, metal, glass and plastic must compete with each other on the basis of environmental quality.

Different materials such as paper, metal, glass and plastic must compete on an environmental quality basis.

Various methods are used to separate waste materials, such as paper, metal and glass.

Pencil cases can be made from a variety of materials such as wood or metal.

Both of these techniques work best for heavier elements such as metals.

A low negative indicates a strong reducing environment, such as free metals.

Some materials, such as metal, may become very hot during warm, sunny weather.