Recording medium

A thermo- or pressure-sensitive recording medium comprises a microporous thermoplastics film having a fibrillar or reticulated structure, preferably produced by stretching the film which contains particles of a filler and optionally removing the filler, and a coloured underlayer. Impact on the microporous film causes it to change from an opaque to a clear state revealing the coloured underlayer. The medium may be used to reveal impact e.g. of a golf ball on the head of a golf club to which it is attached, it may be printed in an impact or thermal printer or it may be used to detect temperature rises above a characteristic limit at which the film becomes transparent.