Thermal grease, also known as thermal grease, should actually be called a silicone paste, which is made of silicone oil and filler.
The silicone paste filler is a very finely ground powder with zinc oxide/alumina/boron nitride/silicon carbide/aluminum powder (which is what we usually see in white).
It should be noted that the “non-volatile” of silicone oil is relative. After a long period of use, some poor quality silicone oil will dry out due to small loss.
These are used in electrical products area, as we all know, we use a plastic enclosure or an aluminum enclosure to protect components and get a nice appearance.