Silicon-free. Apiezon M grease is similar to grease type L, but it contains more wax. Type M is still suitable for very high vacua but not when this requirement coincides with higher than room temperatures. 

Recommended for applications where a grease of moderately low vapour pressure is required, such as for sealing ground joints on the backing side of oil diffusion pumps, for desiccators and cool or cold high vacuum situations.

Grease M has an estimated vapour pressure @ 20 deg. C of 2x10^-9 torr. 

We do not recommend Apiezon M for EM use; columns can get hot and then the vapour pressure of Apiezon M may be too high.