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[729 fx]

A friend recently asked me how do people test the hardness of the rubber sponge.

I believe there is a machine that measure the sponge hardness(in degree) called Durometer. The higher the number - usually the harder the sponge.

I was wondering how does one actually compute the hardness of the sponge? What calculation or on what concept/principles?

Can anyone throw some light on this topic?

[729 fx]

There are industrial (non-table-tennis) standards for measuring the hardness of rubber. 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

An important characteristic of sponge is how hard it is. Hard sponge will give more speed. The disadvantage of hard sponge is more difficult to drive the ball into the sponge (more difficult to loop drive). Soft sponge is harder to control when blocking.

Some of the values the manufacturers gave in degrees while others a description like “Soft”, “Medium”, or “Hard”. Some of the manufacturer does not provide any information on sponge hardness.

[varghese]

I think the manufacturers give the 'soft', 'medium' and 'hard' meaning to not just the sponge, but to the top sheet also. The overall feeling means the rubber feeling.

[729 fx]

You may be right in that sense.

[adriel623]

I think the manufacturers give the 'soft', 'medium' and 'hard' meaning to not just the sponge, but to the top sheet also. The overall feeling means the rubber feeling.

Yep thats what everyone i ask says!

[729 fx]

Some of the rubbers I have seen has the hardness number etched on the back of the rubbers.
What I would like to find out is at what range the degree of hardness do Soft, Medium and Hard covers?

For example, I would term anything from 33 degree and below as being soft.

[ejunkie]

It all depends on who the maker of the rubber is. A 33 degree DHS rubber isn't as soft as you might think!

[729 fx]

Agreed. A DHS 33 degree may be equivalent to a Butterfly 37 degree, I think.

[varghese]

Excellent discussion.

In the case of XIOM, the Omega II Euro has a 40 degree hardness. They mention it as 'extra soft'. All other rubbers have hardness greater than 40 degree.

In my opinion, there is no special equipment used to measure the hardness of the rubber and publish that information. The manufactures do performance test of the rubbers and give a hardness value. It is more of a comparative study between rubbers. The manufactures are interested in the performance, and relate that to some value to help the consumers.

It is like the pillow that we use. In India I have seen the pillow made of cotton. They are hard like rock. Now I see very soft even to the level of calling feather light pillows. The hardness of pillow varies by how you feel when you rest your head on it. Based on that I can give values to the different pillows. In the case of rubbers it is the bounce of the ball.

That's my theory. When I visit some of those factories I can get more info. I will visit some Rubbers factories in India when I visit there soon. I may also visit ESN Germany.

It is okay to continue the discussion by taking 729's opinion that there is a machine to figure the hardness out.