One of the raddest things I own
It really does fit under a T-shirt. Flexible and moves with you very well. I was skeptical about the elbow/arm pads lining up with my super-long arms, but the material is some kind of magical uber-stretchy substance that seems to conform to whoever is wearing it. Haven't taken anything more than minor to moderate spills as of yet, but very, very happy with it so far.