Recently I purchased another set of these double-wall tumblers, which I use for my second cup of coffee in the morning (because it holds less than my first cup and because it retains the heat longer).
I noticed that somewhere there were complaints about these glasses getting 'funny' between the walls of glass. I never noticed it on my previous set - I'm still using one of the two previouly purchased.
To my surprise, on the bottom of the glass now is a round silicone 'thingie' which I assume is to seal the hole. This looks like it is just stuck on. Looks goofy.
Patent applied for in Switzerland. Made in China. I'm not sure where the previous set was made, but this set is thicker around the mouth of the glass; I suppose to decrease breakage, but it is not quite as 'lip-smacking" to the lips as the previous set. Oh, well.