Sponge Info

Most rubber sheets have a layer of sponge underneath the top sheet. For most rubber sheets, you have a choice of what sponge thickness you want.

Thickness

Generally, the thicker the sponge, the faster/spinnier the rubber. On the other hand, thinner sponge can be easier to control, e.g., when blocking. Sponge thickness is measured in millimeters. To loop, you need a sponge thickness of at least 2.0 mm. Players who use short pips rubber to attack also generally use at least 2.0 mm. Since long pips rubber is so soft, it is often used without sponge.

Maximum Thickness

The rules state that the total thickness of a rubber sheet, i.e., the thickness of the sponge and top sheet together, must be at most 4 mm. So manufacturers use the term “max” to indicate that the sponge is as thick as it can be for that top sheet. Until recently, most top sheets were 1.7 mm, so “max” meant approximately 2.3 mm. Now there are rubber sheets with thinner top sheets, so some rubber is available in 2.4 mm or 2.6 mm sponge. Despite this, “max” continues to mean approximately 2.3 mm (the new rubber sheets with thinner top sheets do not use “max” to denote any of their thicknesses).

Hardness

An important characteristic of sponge is how hard it is. Hard sponge gives more speed but can make it more difficult to drive the ball into the sponge, thus making it more difficult to loop drive. Soft sponge is harder to control when blocking.

There are industrial (non-table-tennis) standards for measuring the hardness of rubber and plastic. The hardness is measured in “degrees” and ranges from 0 to 100. The higher the number, the harder the rubber or plastic is. Since this is an industrial standard, the numbers should be comparable across brands (unlike speed, spin, and control ratings). For table tennis rubber, the hardness value is just for the sponge, i.e., not including the top sheet.

For hardness, we report the values that the manufacturers give us. For some brands, this is the hardness in degrees. For others, a description like “Soft”, “Medium”, or “Hard”. And, for some, the manufacturer doesn’t provide any information.