Hardness scales: ESN, DHS, Butterfly and how to compare
The previous section explained what sponge hardness is and why it matters. This one addresses a more prosaic but equally relevant problem: when a manufacturer says its rubber is 47.5°, what does that number mean and how does it relate to another manufacturer's 47.5°? The short answer is that it does not relate at all. The long one requires understanding what each scale measures.
The three dominant scales on the market are ESN's (used by Tibhar, Andro and other European brands), DHS's and Butterfly's. All three employ a durometer — an instrument pressing a standardised tip against the sponge and measuring how far it penetrates — but they differ in the type of tip, the force applied, the measuring time and, often, the point in the manufacturing process at which the reading is taken. The result is that each scale generates its own numbers, coherent only with themselves.
The ESN scale, based on the Shore standard, is the most widespread in Europe. Its usual values for table tennis rubbers run from roughly 35° to 55°. A rubber considered soft sits at around 37-42°; a medium one between 42 and 47°; a hard one above 47°. These ranges are indicative within the scale itself and should not be transferred to others.
DHS uses its own system whose values tend to be lower than ESN's for a similar perceived hardness. A Hurricane 3 labelled 39° DHS is not softer than a European rubber at 39° ESN; in practice, the sensation may be comparable to an ESN value several degrees higher. The difference in protocol — type of durometer, measuring conditions, prior treatment of the sample — explains the gap. Added to this, DHS distinguishes between commercial versions and selection versions (provincial, national), which can present different hardnesses under the same product name.
Butterfly publishes hardness values less frequently and uses an internal scale whose range sits in a narrower band. The Tenergy rubbers, for example, run between 32 and 36° on the Butterfly scale, which corresponds to appreciably higher values on the ESN scale. The company has not published its measuring protocol in the detail other manufacturers have, which makes conversion still more uncertain.
The natural temptation is to look for a table of equivalences allowing degrees on one scale to be converted to another, the way centimetres are converted to inches. Such tables exist — Annex A collects the most complete one available — and they are useful as general orientation, but it is worth knowing what they cannot do. A fixed conversion factor assumes the relationship between scales is linear across the whole range, and it is not: the discrepancies vary by hardness zone and by type of sponge. A table of equivalences indicates the neighbourhood, not the exact address.
How, then, to navigate? Two practical principles. First, always compare within the same scale: when hesitating between two rubbers from the same manufacturer, the hardness figure is reliable for deciding which is softer. Second, when crossing manufacturers, treat hardness as qualitative data — soft, medium, hard — rather than as a precise figure. A player who knows they play comfortably with medium sponges on the ESN scale (42-47°) can look for the equivalent range in DHS or Butterfly by consulting Annex A, but must accept a margin of uncertainty and, above all, confirm the sensation with the rubber mounted on their own bat. The playing implications of each hardness range — what a soft sponge is after, what a hard one demands — are developed in 5.6.