Melamine is a versatile material which resists the spread of fire. It can tolerate heat better than other plastics. It is used in the firefighters' uniforms for the protection of their body from heat hazards. It is also used for making floor tiles, kitchenware, in aeroplanes and buses to prevent the spread of fire.

Thermosetting plastics are those plastics which once moulded, cannot be softened by heating. Two examples are:

1) Bakelite: Used for making electrical switches, handles of various utensils.

2) Melamine: Used for making floor tiles, kitchenware and fabrics which can resist heat. 

Based on the connections between their monomer units, plastics are classified as linear and cross-linked plastics.
$\bullet$ Linear plastics: the monomer units are connected in linear fashion.
$\bullet$ Cross-linked plastics: cross-links exists between two linear or branched chains, forming a three-dimensional network.

This arrangement of monomer units define the properties of polymers. Linear polymers can be bent easily, whereas bending cross-linked polymers is difficult.

A material which is not easily decomposed by natural processes is termed as non-biodegradable. Plastic is generally considered non-biodegradable as it cannot be degraded by bacteria. 
Plastic bags and other plastic items, that we use in our daily lives, end up in landfills and are typically buried. Since they do not degrade, they pose a greater environmental threat than the biodegradable wastes do.