It doesn't change shape, really. It stays in place, even when it's wet. Well...except for the bangs. But that's understandable.

[His fingers curl in a little, giving Atem a brief, gentle squeeze before finally pulling away reluctantly. He feels...warm. Not the same way as he had before Atem had freshened up. No, he just feels satisfied with the fact that they're coexisting in the same space.]

I'll admit that I always imagined it was product, not your actual hair defying gravity.