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Question: I was wondering what material is in contact with the liquid in the cup: stainless or a plastic?
Document: Another reason I don't care for this cup is its tiny liquid flow when the lid is on. In order to drink out of it, when the lid is on, you have to rotate it counter-clockwise and match it up with the markings on the cup. When you do this and try to drink out of it, the liquid comes out -very- slowly.
Great hot/cold cup. Keeps hot liquid hot enough to enjoy for hours. Cold drinks, too. Drink from any place on the lip.
The stainless portions will last forever, and the lid (with all its other faults) is a very simple design that doesn't look fragile. But the slightly loose rubber sleeve doesn't inspire confidence.All that to say - if you're looking for a sealable travel mug that you can actually drink from, there are better options.
It is also not very spill proof. With the lid closed, if it gets knocked over, some of the liquid does dribble out.All in all, it keeps your hot beverages hot, and the cold ones cold. I would recommend with those reservations.
Even for that, though, there are better options! I have both 12oz and 16oz versions of theThermos Nissan JMW500P6 16-Ounce Stainless-Steel Backpack Bottle, Silver, which is EXCELLENT at keeping drinks warm. I can drink half my coffee on my way to work, let the other half sit on my desk for a few hours, come back to it, and even the reduced quantity is still warm when it's in the Backpack Bottle. And that's without any preheating or other fussing!
I bought one of these traveling mugs 5 years ago. Used the 1st one every day for that amount of time, occasionally trying other styles. This one SEALS, this  one keeps coffee HOT for hours. The seal finally wore out. FIVE YEARS of everyday use, everyday washing. Worth every penny. Very comfortable too. Well padded and insulated. Stainless steel interior. If you're on the road a lot, or if you're kind messy, this is the one!
I purchased this and returned it for two reasons. The main reason is the 360 degree lid--while cool in concept--does not allow much liquid at all through. So, you have to tilt your head WAY back to get anything out of it (and off of the road in front of you if you happen to want to use this as an in-the-car mug). The very deep lip on this adds to the problem.
Love this mug, no spillage whatsoever, coffee stays hot, and tastes really good. None of that plastic-y taste you get with most travel mugs. Highly recommended.
Regarding the seal when closed, I've "practiced" sealing the lid (as one reviewer suggested) and lined up the special rectangular tab with the opening symbols (as another reviewer suggested) and it liquid still dribbles out when the mug is tipped. This may not be a big deal - some travel mugs simply have a small opening and don't claim to seal at all, and that's OK. But since this one claims to be "sealable", I think it should, oh I don't know, SEAL?
My Thermos 2610ST2P certainly keeps hot beverages hot! In fact, it is remarkably efficient. The one-drawback is that the liquid does not come out of the 360-degree lid as quickly as I would like. The engineering of the lid ensures an excellent fit, and nomenclature clearly indicates the three positions of the lid - Closed, Open, Remove. Finally, the tumbler is comfortable to hold, well-balanced when resting on a flat surface, and built to last.
Answer: Stainless steel the top of the cup is plastic where the lid attaches and i loved my first one so much  i bought an other one  well  worth it to me at any cost. do not have top fumble the lid open and where to drink out of it....I call it a contractors sippy cup....lol.  hope the helps you out