Does the top lock on? Is it a screw on lid that would not leak if tipped over? Yes, if tipped over it would leak because the slot for drinking does not close. It has a tight fitting rubber gasket to keep the lid tight but it does not screw on.
Does this cup sweat with cold drinks and does the outside get hot to the touch with hot drinks? No sweat whatsoever with cold drinks. With hot drinks, the temp of the outside may get a hair warmer than room temp, but not even warm enough to really notice.
Will the 30 OZ tumbler fit in a car cup holder? What is size across bottom of glass?
Yes it will. The size across the bottom of the tumbler is 2 3/4".
Where is the cup made? Designed in the USA. Manufactured in China