Which technique is commonly used to prevent hair damage during thermal styling?

Using a heat protectant is essential for preventing hair damage during thermal styling because it forms a barrier between the hair and the heat source. Heat protectants typically contain ingredients like silicones or oils that help to coat the hair shaft, reducing moisture loss and minimizing damage from high temperatures. When styling tools like flat irons, curling wands, or blow dryers are used, the high heat can lead to changes in the hair’s structure, such as brittleness or breakage. A heat protectant not only reduces the risk of these issues but also helps to maintain the hair's shine and overall health.

While the other techniques mentioned may contribute to an efficient styling process, they don't specifically address the important task of protecting the hair from heat damage as effectively as using a heat protectant. Sectioning helps in organized styling, heat sealing is more about locking in styles, and temperature testing is about ensuring tools aren’t too hot, but none of these measures offer the direct protective benefits that a heat protectant provides.