Along the same lines as tea-bags, is it possible k-cups have an effect? The keurig machine is already plastic, so does using a reusable cup buy you any benefit?
https://cdn.shopify.com/s/files/1/0601/8783/6659/files/Evolu...
Link is from the FAQ page on aeropress.com.
I can't find the reference now but at one point they discussed why they don't offer an aeropress in stainless steel or glass, and it's basically because of safety (metal and glass transmit heat much more than plastic). Additionally with glass, even pyrex, there is a risk of breakage.