Technically , the retreading consists in the renovation of a tyre replacing the  used layer of rubber by a new one, with similar properties.

When the layer of raw rubber is put on the casing and pressed in a mould (where the layer will have his finale shape), we talk about hot retreading.

When the precured layer of rubber (the pattern is definitive) is applied to the casing thanks to cushion gum, and alltogether is then cured in an autoclave, we talk about cold retreading.

Retreading a tyre consists in replacing some element of a used casing, so that it remains conform with the conditions of use. Retreading is also a repair operation.