First off, the most common name for them is cushions, but I frequently find pool table shoppers refer to them as “bumpers.” It doesn’t really matter because most salespeople know what they mean.
The purpose of rail cushions is to rebound the balls while maintaining their kinetic energy.
In order to maintain their momentum, rail cushions are made from vulcanized rubber. Vulcanization is the process of converting rubber into a more durable material by adding sulfur to uncured rubber. In its natural state, rubber is sticky, but tends to not hold its shape when it warms, or becomes brittle when it gets cold. Commonly used vulcanized rubber products also include: hockey pucks, shoes soles and tires.
Charles Goodyear of tire fame claimed he discovered the process in 1839, but the process of mixing latex to create processed rubber has been around for about 3500 years; much longer than the pool table or the automobile.
But to complicate the matter, not all rail cushions are made exclusively from real rubber. Synthetic rubber can also be vulcanized. Whether the cushions are made from real or synthetic rubber, canvas is often vulcanized into the top of the cushion to control rebound accuracy and speed. This will be readily apparent before the rails have been felted.
Now according to one famous pool table manufacturer, “Not all 100% pure rubber cushions are created equal. Cheap fillers have been used in billiard cushions for years.” Of course they claim to use the highest of the five grades of rubber available.
They add that their “premium-quality rubber is processed with proprietary chemicals and pigments to increase accuracy and produce consistent play.”
Well who doesn’t want to buy products made from the finest raw materials?
“To prevent the tendency of rubber to revert to its natural soft state…” they use special "anti-reversion" chemicals. They additionally claim that this process negates the need for canvas control fabric.
But the reality is that vulcanized rubber is an irreversible process, because vulcanization is generally irreversible. Similar to other thermosets like epoxy, once hardened, it cannot be reheated and reverted back to its original form. The buyer must decide whether or not the manufacturer’s claim is real science or simply sales hype.
My advise for potential non-professional pool table buyers stuck on this important component of the table is to do the test recommended by the Billiard Congress of American (BCA):
“Cushions should react so that they conform under controlled conditions to the three cushion angles prescribed in the “diamond” (or site) system shown below to ± 1 ball width. The speed of the table cushions should be such that placement of a ball on the head spot, shooting through the foot spot, using center ball english, with a level cue and firm stroke, the ball must travel a minimum of 4 to 4 ½ lengths of the table without jumping.”
So to answer to your question, “What are pool table bumpers made of?” It varies from one manufacturer to the next. Pick a company that has been in the business of constructing pool tables for a reasonable amount of time. If you like the look and the price and the table meets all of your other expectations, buy it and get ready to enjoy many years of memorable gatherings with family and friends.