Firstly, like math; English have several ways to do the same thing:

So, risking my answer being perfected (thank god); I will offer my two pence now:

cabelo preso- can be:

                                knotted hair (dado um nó)

                                 tied back in a ponytail (amarrado em "rabo de cavalo" )

                                 braided hair (entrançado, em tranças)

                                 in bun ( em forma de coque)

                Secured with ponytail holder or hair clip--amarrado com "jacaré"; em outros  estados ou outras pessoas podem usar outros nome para jacaré. ou com presilha (clip).

Para cabelo solto- untied hair or flyaway hair (the later with a sense of hair that is loosely touched by the wind...)

Important (maybe) notice: Hair is at they weakest when wet, so brush him with a wide toothed comb. when wet or damp, if you don´t want kiss it goodbye.

PS. I don´t fuss about hair, the notice was only because I deemed important somehow.

See ya.