From experience, Lego are nowhere near water-tight, say nothing about air-tight. The air between the pieces will leak out before you can build a high enough vacuum to pop them apart. I suspect this is by design: air-tight connections probably create enough of an internal vacuum that doesn't come apart with hand-force.
If the push-in joints were air-tight they would be harder to put together as you would be pressurizing the air in each connection. Then the internal pressure would be working against the friction fit to pop them apart again.
I made a mould out of Lego (to make Lego-shaped gummy candies) and with a thin coating of vaseline on the outside, it was indeed water-tight (and silicone-goop-tight too).
I think there were there were beads of water on the outside of the mould, but it was much closer to water-tight than I had imagined, even without the vaseline.
They're astonishingly well made for a children's toy.
They're astonishly well-made for anything. Making bricks that hold together firmly and come apart easily requires micrometer tolerances, and Lego is basically on the cutting edge of plastic manufacturing even today. That's why non-Lego brand bricks are always kinda crappy; no one else can make them as precise as Lego can.
This is being pedantic, but I imagine they probably could, but they don't because it's expensive. An upstart hitting the marketplace without the incredible brand of Lego, plus higher prices would be a monstrous risk.
There are one or two that come close but the precision and variance of Lego blocks is the stuff of myth that professional mold makers talk about on their lunch breaks. You have to really get close to the parts to see how incredible they really are, with the naked eye you won't see enough detail. The trick is repeat accuracy and that's where Lego is far better than their competition.
That said, they've been cutting quality, moving production to China, using cheaper formulation plastic. That's a bad move imnsho. The brand image is quality and people pay for that, if they ever seriously let that go it's going to be game over for them.
Obviously it's easy to say without knowing how frustrating poor quality parts would feel, but I'd take the quality reduction alongside a price reduction, I think. My 4yo loves sets like 31052 (3-in-1 camper), but the next step up in challenging, brand-neutral sets are around AU$400 which is hefty.
Of course, chances are they'll reduce their production costs but maintain the high prices.
I would like to challenge him with the creator expert set of modular buildings. 10246, 10255, etc. But 10255 is US$399 for example.
He already has 31052 and 31051 which I think are excellent 3-in-1 sets. Would love to see more like those. They are about AU$80-120 which is a workable birthday/xmas pricepoint.
That's really not that much (1-999 μm). Keep in mind that sub-1mm is micrometer, and 1mm is a huge distance. I'm sure that LEGO bricks have tolerances of single or low double digits of micrometers...
