As the thermoplastic is heated to above its crystalline melting point (120 °C; 248° F), the crystals disappear. The molecules can then easily slip past each other, so the material flows. During the investigation of atomic energy, the important discovery was made that exposure of some plastic materials to high-energy penetrating radiation can cause permanent crosslinking (inter-molecular joining) of adjacent molecules.

This linking results in the chemical bonding of the plastic structure into a new three dimensional matrix. Once a material has been crosslinked, it will not melt or flow at any temperature. When heated, the crystals disappear as before, but no flow or shape change occurs because the crosslinks act as ties between the molecules. However, the structure remains elastic when the crystals are melted; the material behaves like a rubber.

Products that have been radiation crosslinked exhibit perfect elastic memory. They can be supplied in a deformed or expanded condition. When heated, they shrink for example, to tightly enclose an object over which they have been placed. This makes them ideal for covering a variety of pipes and pipe fittings, as well as wires, lugs, terminals, connectors and other electrical and electronic components.