The use of internal ovens is common in high-temperature–high-pressure experiments. Improving the thermal insulation means better efficiency and lower thermal strain on pressure vessels and feedthroughs, but is difficult when using solid media. The addition of a layer of amorphous solid (glass) in the form of a mixed powder is reported to give a significant reduction (20&percent;–50&percent;) in the power dissipated in a high pressure oven. ©1998 American Institute of Physics.