Occasional heat to straighten natural hair isn’t so bad, but you definitely do not want to rely on it every time you would like to stretch or straighten your hair. Read 7 Lies About Using Heat on Natural Hair
Thankfully there are options to straighten your hair without heat:
Crown Braid n’ Butter
Recently I created my own mix of whipped Shea Butter applied this to my hair and plaited it into two thick goddess styled braided crowns around the circumference of my hair. This essentially left me with nearly straightened/blown out looking hair after I removed my braids the next day. Butters are great when you need some stretch and the thickness of Shea Butter puts in that work. Whip your Shea Butter and try mixing with some of your favorite oils as Shea Butter in its raw form is often way too thick and clumpy. Braids also tend to be more effective at extending your hair then twists tend to be, so when you pair butter and braids, expect magic!
Roller Sets (Flexi Rods + CurlFormers)
Roller sets will give you the appearance of straightened out hair without the need to even touch heat. For the best stretch use flexi rods or CurlFormers as their lengthy design will give you more stretch than a perm rod for example. I highly recommend setting your hair using a styling foam or setting lotion. This will give you longer lasting style, it cuts down on frizz and your hair will have some nice movement. Here’s a video tutorial on how to use flexirods.
Check Out 4 Ways to Create Heatless Curls
Banding is the use of hair ties along the length of your hair to create some stretch. First moisturize your hair. Then separate your hair into at least 4 sections (more sections are likely to give you more stretch). Let your hair set overnight and undo your sections in the morning.
African threading works the same way as banding. The only difference is thread (the same you use for sew in weaves) is used instead. Like banding this method is time-consuming, but the results are pretty incredible and save your hair from heat damage. It will look just as if you just blew your hair out without the need to grab for your hair dryer.