‘衬垫’ (chèn diàn) is a compound noun formed from two characters: ‘衬’ (chèn), meaning ‘to line’ or ‘to serve as backing’, and ‘垫’ (diàn), meaning ‘to pad’ or ‘to cushion’. Together, they refer to a thin layer of material placed between two surfaces to provide protection, support, insulation, or sealing. It’s commonly used in both technical and everyday contexts — for example, in medical devices (like orthopedic braces), machinery (as a gasket to prevent leakage), footwear (insoles), or clothing (lining fabrics).

While ‘衬’ alone often implies a supportive inner layer (e.g., 衬衫 ‘shirt’ literally ‘lining garment’), and ‘垫’ alone suggests something placed underneath for elevation or comfort (e.g., 垫子 ‘mat’), combining them emphasizes function over position: the object isn’t just beneath or behind — it actively separates, protects, or seals. The term carries a neutral, slightly technical register and appears frequently in product manuals, medical instructions, and engineering descriptions.