Table tennis rubber sponge hardness table:

Sponge hardness table

These hardness measurements were done with a specialised foam durometer. Although the durometer measurement are accurate, the sample required for absolute measurements need to be at least 10mm thick, and obviously without a topsheet attached. By testing a series of known hardness samples, and seeing how the readings were affected with only a 2.2mm sample and a topsheet attached, I have adjusted the values accordingly. So the absolute values may not be quite right, but values should be quite accurate relative to each other.

Note: In a few cases I've measured more than one sheet of the same type, so I've included all readings which is useful to see the variations among the sheets.