I used to use those what appear to be these cups and you can buy replacements very cheap on Amazon for about $5. I would buy some of these and then if you melt one somehow, just get a new one. Here's a link: https://www.amazon.com/dp/B07XRTDFF4?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1.

I no longer use these, I switched to the Piro Prone B which has much better cups.