Ceramics made of beryllium oxide. Typically used in multi-stage coolers due to its higher thermal conductivity. The advantages to this material are that it enhances the thermal performance of the TE Cooler as well as makes it easier to assemble because of the high heat conductance. Disadvantages are that it is more expensive and BeO can be toxic when its dust is inhaled. The dust comes from dicing and sanding of the material, both of which are performed on a TE Cooler in its final condition. However, the risks of BeO sometimes prohibit it as an option.