西德研制出一种名为“Frelen”的泡沫聚乙烯吸声材料。这种吸声材料是由三维结构的、密闭的、蜂窝状聚乙烯泡沫制成的,内填以铅丸,以防止材料受压时变得紧实。据称,这种材料只要很薄一层,就有很好的吸声效果,而且不受尘、水、油和其它化学物质的影响。金属薄板复加一层这种材料 West Germany developed a called “Frelen” foam polyethylene sound-absorbing material. The sound-absorbing material is made of three-dimensional, closed, cellular polyethylene foam filled with lead pellets to prevent the material from becoming compacted when pressed. Allegedly, as long as the material is very thin layer, there is a good sound absorption effect, but also from dust, water, oil and other chemical substances. The metal sheet adds a layer of this material