# How Are Micropores Formed in PP Breathable Film? Filler-Free PP vs Calcium Carbonate-Filled PP

> Source: https://breathablefilm.com/news/knowledge-center/how-are-micropores-formed-in-pp-breathable-film-filler-free-pp-vs-calcium-carbonate-filled-pp/
> Author: kh_sales02
> Published: 2026-09-22
> Updated: 2026-09-23

Calcium carbonate-filled PP forms micropores around mineral particles during stretching; filler-free PP creates pores from stress within the polypropylene's own crystalline structure — no mineral filler needed.