Flat Iron Temperature 101: Pick the Right Setting for You

I distinctly remember the first hair straightener I ever used—not my own, but one stolen from my mother. It turned on with a single flip switch, weighed about 15 pounds, and loudly sizzled with each pass. Since then, we’ve come a long way in flat iron technology. Gone are the days of sandwich press-sized contraptions and ceramic-less plates.

One thing that hasn’t changed? The serious hair damage that heat tools can cause. Luckily, today’s flat irons can help limit that damage by offering a variety of settings to choose from. While your instinct might be to jump to the highest temperature right away, fight that urge—there are options for a reason, and depending on your hair type and goals, a lower setting may actually create the best, healthiest result for you.

If you’re not sure what temperature setting to opt for, you’re not alone. That’s why we went to the experts—a lot of experts—to find out the best settings for every hair type. Grab your straightener and a trusted heat protectant (it’s a must), and read on to find the right temperature setting for your hair, plus some extra tips from the pros on how to get that silky-smooth hair we all know and love.

Straight Hair

The experts all agree: straight hair should be ironed on a lower setting. The golden range seems to be between 250°F and 375°F, depending on hair thickness (go lower for finer hair, and higher for thick or coarse textures). More specifically, they suggest starting on the lower end, between 250°F and 300°F, and then adjusting as needed from there. 375°F should be reserved for especially coarse hair. 

“We must remember there is no need for extra heat if your hair is already straight,” says Rashuna Durham. “The flat iron process on straight hair is just to smooth the cuticle and get rid of any of those pesky little flyaways. Always start at a lower level and increase as needed.” That being said, both Azadganian and Killen warn against going under 300°F, as a lower temperature may require more passes of the iron and ultimately cause greater damage.

Given that less heat is always optimal, try and allow your strands to air dry completely before using a flat iron, though Azadganian notes that air-dried hair will likely look slightly darker and have less volume than blow-dried hair. To get some extra volume sans blow dry, opt for a light volume spray like the ones from Ouai or Amika. 

Either way, all our experts emphasize the importance of using some sort of heat protectant before using any styling tools on the hair. For straighter, finer hair, opt for a spray or lightweight cream, like Gisou’s Propolis Infused Heat Protecting Spray, Kérestase’s Resistance Heat Protecting Leave In Treatment, and Morrocanoil’s Perfect Defense Heat Protectant.

Wavy Hair

For wavy hair, go for a temperature between 300°F and 375°F, reserving between 350°F and 375°F for coarser hair types, virgin hair, and chemically treated (but not damaged!) hair.

Wavy hair of a finer density should prep with a lightweight heat protectant spray, like Living Proof's PhD Heat Styling Spray or Drybar's Hot Toddy Heat Protectant Mist, on dry hair. Meanwhile, wavy hair of a thicker density or more coarse texture benefits from a more emollient heat protectant like a serum or balm applied to damp hair prior to air drying. We’re fans of Amika's Blockade Heat Defense Serum. 

Again, air drying is optimal here—the name of the game is avoiding unnecessary heat damage. Pro tip: “To help elongate waves for easier flat ironing, thoroughly detangle using a heat-resistant fine tooth comb immediately preceding your flat iron,” Killen suggests. “Take a section of hair, put your comb in, and follow your iron behind the comb.”

Curly Hair

Curly hair requires a little more heat to smooth out the curl pattern, so experts suggest using a flat iron at a temperature between 325°F and 410°F. Things get a bit dicier when it comes to finding the right temperature for curly hair: Go too hot and you might alter the natural curl pattern, creating inconsistent texture and causing heat damage. But go too cool and you might not get the silky-smooth result that flat irons are capable of creating. Again, temperature choices within that range should be based on texture, density/thickness, and amount of hair damage.

All our experts agree, though, that curly hair requires different prep work than their straight- and wavy-haired counterparts. Curly hair should be blown out before taking a flat iron to it. It allows the strands to become pre-stretched, so there isn’t as much direct heat from the flat iron and you need less passes of the iron to achieve your goal. Killen suggests using a moisture-sealing heat protectant on damp hair, layered with a heat protectant spray or serum on dryer hair. Rahua and Mizani both make great moisture-sealing heat protectants.

Meanwhile, Durham says it’s important to remember that, when trying to straighten curly hair, it should be done on freshly cleansed and conditioned hair. Curly hair tends to have more product buildup, so making sure hair is clarified of any previous buildup before reaching for the flat iron allows you to transition from curly to straight with less damage.

Coily Hair

As expected, coily hair requires the highest temperature to straighten it out due to the very strong curl pattern. Our experts suggest between 375°F and 450°F to get those coils silkened out. As always, err on the side of caution (especially for finer, chemically treated hair) and raise the temperature as needed. Regardless of density, Azadganian says to keep in mind that flat ironing over time can reduce and even damage the natural state of the curl pattern, so keep the heat damage to a minimum.

Those with coily strands should definitely blow dry beforehand. If allowed to air dry, your coils will do exactly what they do best (coil into each other), making it harder to detangle and creating a situation in which the flat iron would have to pass over the strands too many times. When blowing out coily hair, Killen suggests using a natural boar bristle brush, preferably one with vents so the air can pass through. Boar bristles will grip the hair, providing tension that helps to distribute natural oils, moisturizing products, and heat protection down the coily hair strand. Some of our favorite heat protectants for coily hair include Briogeo's Farewell Frizz Heat Protectant Crème and Olaplex's No. 7 Bonding Hair Oil.

Killen also suggests using your thumb and a fine tooth comb to create tension in the hair, particularly at the hairline and root area, and tap your flat iron to ensure the roots have a matching smooth texture to the ends. Meanwhile, Durham advises tying hair up at night with a silk or satin scarf to extend the style. It’ll allow hair to retain moisture, keep frizz at bay, and keep strands shiny without being greasy. As for Azadganian, he suggests using a healing conditioner or restorative mask to protect day-to-day styling, while Rëzo recommends setting coily flat-ironed hair with a roller set to finish.