Abstract: Glass is thermally treated by contacting the glass with a gas-fluidized particulate material of non-compacted particle structure which is such that the apparent density of the particles is less than the actual density of the material forming the particles. The buoyant particles constitute a gas-fluidized bed in a quiescent uniformly expanded state of particular fluidization, and the material of the particles and the temperature of the bed are selected so that the heat transfer coefficient of the bed is sufficient to produce a desired thermal treatment, for example thermal toughening of hot glass.