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.
If you are wondering how does one actually compute the hardness of the sponge? What calculation or on what concept/principles? Below information may shed some light for you on this topic.
Industrial Standards in Measuring Rubber Hardness
There are measuring standards in the rubber industry to gauge the hardness of different rubber. The hardness of the rubber is gauge in “degrees”. The ranges for the degree is from 0 to 100. The higher the number, the harder the rubber is. Due to this is the measuring standard being used in the rubber industry, therefore the number of degree should be comparable across brands. While for the rubber being used in the sport of table tennis, the hardness value is just for the sponge.
A vital sponge characteristic is the level of hardness of it. The harder the sponge is, the more speed it will give. For hard sponge, the disadvantage is it’s more difficult for player to drive the ball into the sponge which mean they are more difficult to perform loop drive. While for soft sponge, it is more difficult to control when doing blocking.
Some of the values the manufacturers gave in degrees while others categorized them into 3 main categories like Soft, Medium, or Hard. Also there are some manufacturers do not provide any information on sponge hardness at all.
For your information, the manufacturers give the ‘soft’, ‘medium’ and ‘hard’ meaning to not just the sponge, but to the top sheet as well. The overall feeling means the rubber feeling.
Some of the rubbers I have seen has the hardness number etched on the back of the rubbers. So how can you find out is at what range the degree of hardness do Soft, Medium and Hard covers?
For example, some people term any number from 33 degree and below as being soft. But in fact it all depends on who the maker of the rubber is. A 33 degree DHS rubber isn’t as soft as you might think! A DHS 33 degree may be equivalent to a Butterfly 37 degree.
In the case of XIOM, the Omega IV has a 40 degree hardness. They mention it as ‘extra soft’. All other rubbers have hardness greater than 40 degree.
Equipment to Gauge the Hardness?
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 certain places you may 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 may be able to get more info. Nevertheless, it is completely okay to continue the discussion by taking some people opinion that there is actually a machine existed to measure the hardness out.