A lost circulation material is placed in a cavity. The cavity is defined by an inner bore of a cylindrical wall, intermediate of a piston and a screen. A distance between the piston and the screen is defined as the height of the cavity, which is adjustable. The piston is slid longitudinally, such that the piston comes in contact with the lost circulation material. The lost circulation material is heated to a specified test temperature mimicking a downhole temperature. A compression test is performed on the lost circulation material. The compression test includes flowing a test fluid into the cavity and applying force on the piston to pressurize the test fluid to a specified test pressure mimicking a downhole pressure. The force on the piston is released. The pressure of the test fluid and the height of the cavity are measured throughout the compression test.