What is industry-grade polypropylene and where can I get it?

https://theconversation.com/polypropylene-the-material-now-recommended-for-covid-19-mask-filters-what-it-is-where-to-get-it-149613

How can we implement the 3 Nov 2020 updated guidance from Health Canada on including a third, middle layer, preferably of polypropylene? This article explains what to look for and how to work with this inexpensive washable fabric-like material.

Charles de Lannoy (engineering), Scott Laengert (chemistry), Catherine Clase (epidemiology) and Barry Diamond (textile distribution) from the Cloth Mask Knowledge Exchange (all) and the McMaster Centre of Excellence in Protective Equipment and Materials (Charles, Scott, Catherine).