PCB Test Elastomer

https://www.rubberinterposer.com/products/elastomeric-film/

PCB Test Elastomer, often made of silicone rubber, is a versatile material used in various applications such as electronic device assembly, vibration dampening, and sealing. Its elastic properties allow for conformal contact in fine pitch applications, making it ideal for use in fine pitch test sockets and as a contact interface in electronic testing and packaging.