Straight from www.aeropress.com:

Exclusively designed for use with AeroPress Original, Go and Clear coffee makers, our paper micro-filters are an essential part of the brewing process.  High quality paper absorbs bitter tasting oils while micro-sized holes filter and catch fine particles, stopping them from passing into the cup. Unlike French press coffee brewers, they allow for finer ground coffee and ensure a consistently smooth, grit-free cup of coffee.

Not compatible with AeroPress XL coffee maker. Click here if looking for XL Paper Micro-filters.