Thermal conductivity in either the ON and OFF state of a heat switch is affected by temperature – the thermal conductivity of stainless steel and helium gas varies with temperature. Importantly, steel will determine the OFF-state conductivity, and helium gas the ON-state conductivity. Conductivity will also be affected by the switch’s geometry.

A typical standard He4-filled switch will have an OFF-state conductance of around 3mW between 4 and 30K, and around 10mW between 4 and 45K. It’s switching ratio will be around 500.

If you need the cool to below 2K, the heat switch will be filled with helium-3. We can build specialist switches which are  optimised for low OFF-states for applications (down to 50mK or below).

For applications which need to cool down to a few mK, we have achieved a low µW conductance with high performance designs. These switches are usually at least 10mm long but can operate horizontally or vertically.