[the8472]

There's a 4th layer: The whole thing is vacuum-wrapped in epoxy-fiberglass composite to catch spall.

[rattray]

Because I imagine I wasn't the only one with no clue what "spall" was:

> Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball bearing)

https://en.wikipedia.org/wiki/Spall

[nkozyra]

Odd that the video doesn't seem to catch spall then.

[tyingq]

Catching spall on the back side of the barrier is the important bit.

[cellularmitosis]

Why? Does the spall have enough energy to hurt someone?

[iSnow]

jagged splinters with sharp edges being ejected at high velocity - what could go wrong?