When I think of "heavy duty," I think the liner would be substantial or thicker or tougher than a regular liner - unfortunately, that is not the case with this liner. In fact, it's much thinner than the one I replaced it with. That being said, I've only taken one shower with it and I cannot attest to its resistence to mildew - time will tell. As far as the "heavy duty" part, I would not buy this again - but...that could change depending on the mildew part. It's a THIN, gray shower liner.