Jason Isaacs, who will be portraying Captain Gabriel Lorca on Star Trek: Discovery, shared a video of getting a lifecast made.
A lifecast is a mold that creates “three-dimensional copy of a living human body, through the use of molding and casting techniques,” definition courtesy of Wikipedia). Any part of the body can be lifecasted, and in the case of Isaacs, the lifecast being created was of his head.
In the video, seen here, watch Isaacs go through the somewhat claustrophobic process.
Source: Jason Isaacs Instagram Account