“覆盖物”用英语怎么说？

脑体周围有3层分离的覆盖物.There are three separate coverings around the brain itself.春天我们移去游泳池的覆盖物.In spring we uncover the swimming pool.疏松的覆盖物在土壤表面起了隔热的作用.A loose mulch acts on the surface as an insulator....