The launch debris photos clearly show that the "foam" or whatever it was was intact after hitting the wing. I personally don't believe the "foam" theory, or that it came from the external tank. I think it was a solid chunk of material that struck the wing, gouged a rut down the length, and passed away behind the shuttle mostly intact. The impact cloud shown in the launch video IMO are pieces from the wing itself.

I believe the chunk of material that hit the wing came from the solid rocket booster, because it appeared to be the same color. In fact it contrasted sharply with the color of the external tank, strongly suggesting that it did not come from there. It was not foam that hit the shuttle.