Particulate material suitable for use as a filler in the heat-sensitive recording layer of a heat-sensitive recording paper comprises an amorphous silicate having a composition represented by the following oxide molecular ratio: wherein M represents at least one member selected from the group consisting of calcium, barium and zinc, or a product obtained by partially neutralising said silicate with carbon dioxide, said material having a BET specific surface area of 10 to 70 m 2 /g and a bulk density of 0.14 to 0.30 g/cc and also having such a secondary particle size distribution that secondary particles having a size smaller than 4 µm, as determined by the centrifugal precipitation method, constitute at least 70 % by weight of the total particles.