"垫层橡胶" can be translated as "cushion rubber" or "underlayment rubber" depending on the specific context and usage.
"Cushion rubber" is often used when referring to rubber material that provides cushioning or shock absorption, such as in some engineering or construction applications.
"Underlayment rubber" might be more appropriate when describing rubber used as an underlying layer or base, particularly in flooring or roofing systems.
In most general cases, "cushion rubber" is a suitable and commonly used translation.