My guess is that Blast Proof won’t protect you from the base impact damage (of course, just like with the other elements) but it negates the explosive splash damage. I could be wrong… just kinda guessing! When I take a Harold to Oney for example, I see damage being done to him, but also see RESIST pop up which I am assuming is the splash damage being resisted by him, and I’m just assuming Blast Proof shields have the same mechanic.
Edit: hmm hadn’t considered “pure splash” weapons. I don’t think I’ve ever tried a KerBlaster against Oney, I may go do some experiments on him later.
Edit2: did some quick and dirty testing… it looks like Oney ends up taking 1/2 what the damage on the item card says, but I had my BAR on and Axton’s skills were active and such so the numbers might be fudged a bit. KerBlaster damages him, direct or not. If a KerBlaster does 500,000 on the card, he takes about 250,000 from the projectile (disregarding the grenade the KerBlaster releases) as opposed to other enemies taking almost a million and a half because of all the extra splash (“deals extra explosive damage”). He takes about 3 million from a 6 million damage Nukem. He has some complex damage-reduction formula depending on the explosive weapon hitting him I guess.
Anyway, I now don’t think he has the same mechanics as a Blast Proof shield because those shields don’t seem to perform as well as Oney does, heh.
(Edit3: for my troubles Oney dropped a Judge and Wot dropped an underleveled Emperor while I was on my way to Oney. ;))