sheathing       
noun [ C or U ] uk/ˈʃiː.ðɪŋ/ us/ˈʃiː.ðɪŋ/
 护套
a close-fitting covering designed to protect something
  The frame is covered by a glass and metal sheathing. 框架用玻璃和金属护套覆盖着。 
 The dome's exterior has been covered with protective concrete tiles and copper sheathing. 圆顶的外部用保护性混凝土瓦和铜护套覆盖。 
 See: sheath
 - More examples
 - Nails were used to put down roof sheathing.
 - A single copper wire is surrounded by layers of plastic insulation and sheathing.
 - The cables are protected by stainless-steel sheathings.