I seem to recall from a quick google the other day that the consensus on exoterra was untempered (and there are quite a few people talking about drilling these things) - I think I googled "drill exoterra terrarium" or something like that! Someone said they phoned exoterra up, and the person on the other end said (rather contradictory...) that the glass was tempered, but you could drill it...! Of course, it's possible they've changed glass.