How to keep the humidity from messing my hair up?

My hair hasn't been relaxed in over a year. During the winter time it was fine when ever I flat ironed it out but now that it's getting crazy hot, whenever I flat iron or curl it, it just poofs up! I was thinking about getting twists for the summer so I don't have to deal with heat in my hair everyday but for right now does anyone have any tips on how I can prevent the humidity from causing my hair to poof up