# Flat Iron Temperature and Passes: The Science Behind Lasting Keratin

**By 365 SUN Editorial** · 2026-10-26

Two stylists can use the same keratin and get completely different results. The difference is almost always in the **sealing stage**: iron temperature, section size and number of passes.

## Why heat matters

Heat drives the treatment into the cortex and sets the new bonds. If the iron is too cool, the product stays on the surface and washes out in weeks. If it's too hot, you risk scorching the cuticle and getting a stiff, brittle finish.

## Temperature guide

-   **Bleached or very fragile hair:** 180–200°C (356–392°F)
-   **Color-treated or medium hair:** 200–210°C (392–410°F)
-   **Virgin, coarse or resistant hair:** 220–230°C (428–446°F)

## Sections and passes

Work in **thin sections, about 1 cm wide**, so heat gets through evenly. Use 5–10 slow, steady passes on each section, going a little higher for resistant hair and lower for fragile ends. Keep the iron moving, since stopping in one spot causes hot spots.

## Dry before you seal

Hair must be **100% dry** before ironing. Leftover moisture boils inside the fiber and damages it. That's also where the steam and "frying" sound come from.

## The right product for the job

The [Brasil Cacau Thermal Reconstruction 1000 ml](https://www.brkeratin.biz/products/brasil-cacau-brazilian-thermal-reconstruction-1000-ml) is designed for salon volume. For the full protocol, use the [Brasil Cacau Reconstruction Kit](https://www.brkeratin.biz/products/brasil-cacau-reconstruction-kit-big-3-products), and see the [Application & Technology Guide](https://www.brkeratin.biz/products/reconstruction-application-and-technology-guide-digital) for step-by-step technique.

Master the iron, and your clients will come back for results that last months, not weeks.

**Tags:** Brasil Cacau, flat iron temperature, keratin passes, salon technique, thermal reconstruction

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> Source: [BR KERATIN](https://www.brkeratin.biz/blogs/news/flat-iron-temperature-and-passes-the-science-behind-lasting-keratin)