We have developed a method for measuring the heat capacity of insulating powders as they interact with a gas under pressure. The method is suitable for pressures up to 700 kPa and temperatures from 1.8 K to 300 K. It is based on a previous technique for measuring the heat capacity of powders by compressing them into copper-encased pellets, and it is designed for use with a Physical Property Measurement System (PPMS) from Quantum Design. In the new method, the pellet is sealed in an aluminum DSC pan in a controlled atmosphere prior to the measurement. To determine the method's accuracy, we measured the heat capacity of two samples of calorimetric standard benzoic acid. One sample was sealed in 690 kPa nitrogen gas and the other was sealed under vacuum. We conclude that the accuracy of the new method is comparable to that of standard measurements on samples not sealed in DSC pans. (C) 2019 Elsevier Ltd.