Starbar type HD protection tubes are made of high-density recrystallized silicon carbide. With a nominal density of 2.52 g/cc these permeable tubes (~21% porosity) are able to survive severe environments, and withstand very high thermal shock.

HD tubes may be used at temperatures up to 1500ºC continually, and up to 1600ºC for short duration. HD tubes are manufactured open both ends.