Thermally responsive record material comprises a support having provided thereon in substantially contiguous relationship in one or more layers an electron donating dye precursor, an acidic developer material, a sensitizer, and a binder therefor. The sensitizer comprises at least two components, the first component comprising 2,2-bis(4-hydroxyphenyl)-4-methylpentane and the second component comprising a mixture of dimethyl terephthalate and 1,2-diphenoxyethane. The first component is preferably in a weight ratio of from 1:2 to 2:1, more preferably 1:1, relative to the second component. The second component comprises from 50 to 70%. dimethyl terephthalate. The sensitizer is prepared by admixing the first component and the second component and grinding the sensitizer to a particle size of less than 1 micron.