underlay
noun [ U ] uk/ˈʌn.də.leɪ/ us/ˈʌn.dɚ.leɪ/
（起保护作用的）地毯衬垫
thick material put between a carpet and the floor for extra comfort and to protect the carpet
（尤指可以透过上层材料看到的）下层材料，衬里
a layer of material that lies under another one, especially when it can be seen through the top layer
The dress was black lace with a blue underlay showing through. 那件裙子是用黑色蕾丝和若隐若现的蓝色衬里做的。