For the following NIOSH filter designations N stands for Not resistant to oil. R stands for Resistant to oil. P stands for oil Proof.

• 根据NIOSH对过滤材料的分类定义，N：不适合油性的颗粒物，R：（适合非油性颗粒物）对油性颗粒物由阻隔作用；P：（适合非油性颗粒物）对油性颗粒物防护作用。