From the article: "I quickly noticed how the room got it name as the walls and floor are completely covered in rubber over a soft cushion that was meant to absorb the blast."
The seats in the room also have seat belts. Looks like the room's designers expected a violent experience.
So I am not being facetious when I say I don't understand I I guess your comment makes sense, but honestly... I still don't understand. The rocket explodes, a massive shockwave of expanding gas gets pushed down the chute into the middle room. The actual protected room has a vault-like door, is on springs, has massive padded chairs with seatbelts. That I get. But how does rubberizing the middle room help? How much of the shockwave can it possibly absorb?
I'm not rhetorically trying to say it's useless. I'm perfectly happy to admit that NASA's engineers have a better grasp of this situation than I do. I just don't get how it helps.
Perhaps this is for the safety of the occupants. If they get thrown out of their harness they don't bang against a metal/concrete wall but a little softer material. Though why this is not even softer material I don't understand.
I think this is to avoid that split-second when hard walls would create a concussive shock. That shock would make the door ring like a bell and emit a very loud noise that might deafen the ground crew in their secure room.
The room was supported by springs according the article. It also said the blasts rivaled small nuclear explosions. If something that big goes boom right over you, those springs are going to be tested. I assume the rubber helps prevent the room from bottoming out should the springs be insufficient. If anything, I think they didn't know what to expect, so they planned for the worst.
Also, that small, 24-hr safe room was lacking in 24 hours worth of amenities, like a bathroom and water supply. But I guess being thirsty or having to urinate is better than exploding.
According to the article, there actually is a toilet (behind the camera)... and supplies for generating oxygen and filtering air, which suggests it's pretty likely there's a bit of water etc too.
If I had to guess, I'd say that it's a way of providing some level of protection while you're still on your way to the truly safe space. That is, if there's an explosion while everyone is still sprinting down the final hallway, the rubber walls could turn make things a little less bad. (Heck, if there were multiple explosions, the rubber might be enough to let you recover in time to get to your seat in the vault before the whole thing goes up.)
The seats in the room also have seat belts. Looks like the room's designers expected a violent experience.