Abstract The Planck sorption cooler cold end utilizes Joule–Thomson expansion of hydrogen to achieve temperatures below 18 K. Porous stainless steel sintered elements function as the J–T restriction. We report the flow characteristics of these porous flow restrictors, as a function of temperature over the range 19–300 K at constant pressure, and as a function of pressure at 1.4–5.5 MPa (200–800 psi) at constant temperatures of 19 and 300 K. The J–T restrictors were fabricated in three separate batches, using the same process and materials. Some comments are made regarding the uniformity of results from various fabrication batches.