Thermoplastic compounds are composed of long, straight and branched chains of molecules in a random arrangement. The strength of these plastics depend on the distance between the molecules and the crystalline structure of those molecules. Crystals form where the chains of molecules come close together. It is these crystals which provide most of the plastic's strength.

When thermoplastic material is heated, these crystals disappear. While in this heated condition, the material may be formed into almost any desired shape. When the material is allowed to cool, the crystals reform again providing strength to the plastic's new shape.

During the study of atomic energy it was discovered that when some plastic materials were exposed to atomic radiation it caused a permanent inter-locking or joining of adjacent molecules. This crosslinking of molecules created a strong three-dimensional chemical bond within the plastic without making the plastic radioactive.

ICO RALLY heat shrinkable tubing is the practical application of this knowledge.

When you extrude special thermoplastic formulations and form it into a tube, crystals will form where the molecules come close together as the plastic cools. Then if you expose this tube to irradiation, you create a new three-dimensional chemical bond between the molecules within the plastic formulation. This tube, when hot, can now be increased in size by applying pressure inside the tube. While expanded and under pressure, the tube is then cooled allowing the crystals to reform and lock-in the new stretched tubing shape. This is the form which heat shrinkable tubing is supplied to customers. When the customer applies sufficient heat to the tubing, the crystals will once again disappear and the tubing will try to return to its original shape, causing the tubing to shrink tightly, conforming to the object's shape over which the tubing has been placed. When the heat source is removed, the crystals reform giving strength to the new tubing shape.