The working life of a rubber: what degrades and why

A rubber does not last forever. From the moment it is unwrapped, its properties begin to change. The process is slow and invisible at first, but cumulative: what the player perceives one day as a loss of grip or of liveliness is the result of weeks or months of chemical and mechanical transformation. Understanding what degrades — and by what mechanism — helps to distinguish real wear from imagined wear and to know which factors accelerate it.

The most exposed component is the topsheet. Its surface comes into contact with the ball, with the air and, if the player does not protect it, with light. Rubber is sensitive to oxidation: atmospheric oxygen progressively breaks the bonds of the polymer chains and reduces the elasticity and adhesion of the surface. Ultraviolet radiation accelerates that reaction. A rubber kept in a closed cover ages more slowly than one left in the open on the living room table, and the difference is not trivial. In rubbers with a tacky topsheet — the “Chinese” type — the loss of surface adhesion is especially visible: the ball stops sticking when rested against it without force, a sign that the surface plasticisers have evaporated or degraded.

Plasticisers are, in fact, a key factor. The formulation of the rubber includes compounds keeping it flexible and elastic. Over time, part of those compounds migrates towards the surface and evaporates. The process is called exudation and is irreversible: the rubber hardens progressively, loses its capacity to deform on contact with the ball and reduces both its grip and its elastic response. Heat and humidity accelerate the migration; extreme cold slows it but can make the material brittle.

The sponge suffers a different deterioration. Its cellular structure — the small air bubbles described in 4.2 — undergoes compression cycles with every impact. With repeated use, the cell walls lose their capacity to recover: the sponge becomes less reactive, returns less energy and the catapult effect — covered in 2.4 — is attenuated. It is a mechanical fatigue analogous to that of a spring that has worked thousands of times. The speed at which this occurs depends on the hardness of the sponge, on the intensity of play and on the thickness: a thicker sponge has more material absorbing the punishment, but also more volume subject to fatigue.

Both processes — chemical degradation of the topsheet and mechanical fatigue of the sponge — occur in parallel but at different rates. In a player who trains frequently, sponge fatigue may be the limiting factor. In a rubber that goes months without use, oxidation and the loss of plasticisers dominate. In practice, both mechanisms usually contribute to the result the player perceives: the rubber no longer responds as it did.

A third factor, less evident, is the degradation of the bond between topsheet and sponge. The industrial adhesive joining them — described in 4.4 — can lose adhesion over time, especially at the edges, generating micro-areas of lifting that alter the response of the assembly. It is not the main ageing mechanism, but it contributes in rubbers with many hours of use.

The practical signs allowing the state of a rubber to be diagnosed and the criteria for deciding when to replace it are addressed in 7.5 and 13.7. The conservation measures that slow the process — cleaning, storage, protection — are detailed in 13.5 and 13.6. What this section aims to make clear is that degradation is neither a manufacturing defect nor an accident: it is an intrinsic property of the materials making up the rubber. Every rubber has an expiry date; the question is not whether it degrades, but how fast and by which route.