Never done these bags, but polypropylene is going to melt around 330 F. This stuff has a low press temp compared to others, but have never tried it. Limited colors. https://www.cutterpros.com/specialty-materials-polybag-flex-for-polypropylene-bags
I have a bit of brand loyalty gong on with Siser. On one of there forums they state this:
http://www.siserna.com/heat-apply-htv-heat-sensitive-material/
Maybe someone else has actually done this.