We did a study on glass top humidors using colored smoke bombs:

http://http://www.cheaphumidors.com/...-top-humidors/

I agree, SOME glass top humidors are sub par and leak. I got a sample once where the glass imply sat in a groove on the top lip, no seal at all. I always expect a small amount of air exchange in any wooden humidor, which turns out to be a good thing as it cuts down on the mildew smell. However, glass top humidors should still be able to maintain humidity fairly easily.