Do you know how your reusable one compares to these PE lined paper ones?

If it's one of the recently trendy 'bamboo' cups, I'm fairly certain most of them are made of predominately with melamine.

https://www.chemistryworld.com/news/reusable-bamboo-mugs-lea...

> Overall, the BfR tested 228 bamboo mugs for formaldehyde and 180 for melamine. In each case, more than 35% of the cups released harmful substances in amounts that surpassed safety limits. Moreover, the amount of melamine – but not formaldehyde – the mugs released increased with repeated exposure to hot and slightly acidic liquids.