I sent the Crasche folks an email asking for data documenting the performance of their product. I received the following results as part of a brochure:

LACROSSE CROSS-IMPACT TEST RESULTS (these appear to be stick-to-head):

Sample # Impact Location Cross Velocity (MPH) Severity Index Peak G

Bare Headform Side 38.19 1051 188

Size Small Side 39.94 68 49

Size Large Side 38.64 8 24

LACROSSE BALL IMPACT TEST RESULTS (these appear to be ball-to-head):

Sample # Impact Location Ball Velocity (MPH) Severity Index Peak G

Crosse BXX 1 68.34 278 179

Crosse BXX 2 69.3 208 146

Crosse BXX 3 70.75 294 186

The following sentence was also included in the reply: "Note - these tests are for impact coming onto the head. In a drop test, which simulates a head on collision, a 9 mph event showed an impact reduction of about 25 %."

For reference, I remember reading somewhere that football helmets tend to increase impact duration from about 3 ms to about 8 ms. Assuming uniform force distribution over the duration of the impact, this amounts to ~60% reduction in peak acceleration (over whatever force domain that acceleration is correct for.) Crasche seems to guard effectively against forces similar to that of a lacrosse stick being swung at the head. Unfortunately, the results of the second test don't really tell much about the usefulness of the hat, as the Crasche folks seemed to be satisfied with concluding that it's effective based on seeing a Severity Index (I assume this is based on the head injury criterion?) <300 when taking a lacrosse ball to the head, despite the huge accelerations.

Regarding the drop test - 9 mph gives around 137-82g of acceleration against a hard surface, assuming impact duration of 3-5ms. So we're looking at 6700-4000N (human head weighs around 5kg). In this domain, we can compare the 25% advertised reduction against the ~60% ballparked estimate for force reduction due to a football helmet.

In summary, the performance appears to be inferior (in terms of pure linear acceleration reduction) to a sports helmet, as one would expect. The hat appears to be more effective against object-to-head impacts (involving smaller forces) relative to impacts that result in the head being brought to a halt from motion (involving larger forces) - perhaps the crushable elements providing the resistance are crushed by the larger forces? My gut says that the performance in a vehicle collision will probably bring the head to a halt against a relatively immobile object, so the hat won't do much of anything as the crushable bits are crushed too fast to be effective.