I did some research and found that heat protection sprays are used to moisturize your hair so it doesn't get damaged. If you're a regular reader you know my oil of choice to moisturize my hair: coconut oil! It's inexpensive, smells divine, and it works!
I used my DIY heat protection for hair while my hair was wet, but you could also use it on dry hair. What I do is warm some coconut oil by rubbing it between my hands. Then I rub my hands on my head to distribute the oil everywhere, especially the highlights on the top of my head. When my hair is dry, I use my flat iron as usual.
My hair isn't greasy at all, and it feels so soft! I think my hair actually got smoother with the coconut oil in it versus not using any heat protection spray. My hair even stays smooth and straight after sleeping all night!
You can also try one of the following oil to protect your hair from heat:
Argan oil is a dry oil, but grapeseed oil and olive oil will probably make your hair too oily. You'll have to experiment with them for yourself.
UPDATE I've been using coconut oil as a heat protection "spray" for several weeks now with blonde and red highlights in my dark brown hair. My highlights are healthy and look amazing. My hair is smoother and straighter, and it lasts two full days after I straighten it! I do spritz a teeny tiny bit of argan oil on my hair just after straightening and brush it out. Too much argan oil and your hair will be greasy the next day, so go lightly.
UPDATE I've been using coconut oil as a heat protection "spray" for several weeks now with blonde and red highlights in my dark brown hair. My highlights are healthy and look amazing. My hair is smoother and straighter, and it lasts two full days after I straighten it! I do spritz a teeny tiny bit of argan oil on my hair just after straightening and brush it out. Too much argan oil and your hair will be greasy the next day, so go lightly.