inner envelope

例句：

1. 1. The package was carefully placed inside the outer envelope.
   这个包裹被小心地放在了外层的信封里。
2. 2. She carefully folded the letter and put it inside her inner envelope.
   她小心翼翼地折叠好信，把它放进了内层信封里。
3. 3.The designer used a unique inner envelope design to enhance the product's appeal.
   设计师使用了独特的内层信封设计来提升产品的吸引力。