Apparatus (10), for testing samples of friction material (31, 32) in rubbing contact with a surface (33) of a rubbing element (34), comprises a table (12) for supporting the rubbing element and a load cell (16) for sensing the load imposed by the frictionally coupled rotating samples from which the coefficient of friction can be determined. To make the tests repeatable rapidly and with identical starting conditions cooling means (40) is interposed between the rubbing element and table. Cooling means (40) comprises a fluid cooled heat exchanger (41), conveniently cooled by local main supply water supplied at its natural temperature, and thermoelectric cooling means (75). The thermoelectric cooling means consists of an array of planar peltier cooling elements which develops a temperature gradient there across which, with reference to the heat exchanger temperature, is able to cool and re-cool the rubbing element to temperatures as low as -25 °C within a matter of minutes. To ensure the friction material and rubbing element are not contaminated by water condensed from the atmosphere an enclosure (60) is formed around them and kept at positive pressure by dry, inert argon gas.