"We are preparing materials" 是表达准备材料的常用说法。
其中 "preparing" 是 "to make something ready for use or for a particular purpose" 的意思，而 "materials" 是 "the things that are used to make or do something" 的意思。
一些英文例句及其中文翻译如下：
We're preparing materials for the meeting next week. (我们正在为下周的会议准备材料。)
The teacher is preparing materials for her lesson. (老师正在为她的课准备材料。)
We need to prepare materials for the construction project. (我们需要为建筑项目准备材料。)