We've been using these mugs for about 6 months and think they are about the best thermal coffee mugs ever. The cap locks securely - I've even put a full mug in my purse with no leaks/spills. Unlike many of this type of travel mug, the sip area doesn't dribble onto your shirt. I put them in the dishwasher and have not had any trouble with deformed rubber rings or leaks.
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