The Hydraulic Press Guy is back and this time he's turning his attention to helmets. There's probably not much that can be learned scientifically from this (especially as it's a sponsored video from Specialized) but it's still satisfying to watch mountain bike helmets get the crushing treatment.
In the video, he compares a Specialized Ambush (0:45) to a supermarket special helmet (3:30) with a 10-year-old motorbike helmet (4:40) and military helmets (7:30) thrown in for good measure.
Again, take these with a pinch of salt, but the modern mountain bike helmet performs admirably well, only starting to break under a pressure of around 1,500kgs (3,300lbs), the equivalent of a small car resting on top of it. For comparison, the cheap helmet was around 800kgs (1,760lbs). This is hardly a real-world test, and you definitely should not base your next buying decision around it, but it's still interesting to watch what total failure looks like.