Stainless Steel Insulated Coffee Cup with Lid 350ml 5 "Dishwasher proof?" Mr Holmes 29 September 2015 Hi, I have one of these and highly approve. As others have said it is leak-proof and keeps warm for a couple of hours at least. Can anyone advise whether I am okay to put it in a dishwasher, or will this wear the rubber seal? Many thanks. A note from the team We've checked this for you and can advise it's not dishwasher safe, we hope this helps.