A heat protectant is something that adds moisture to your hair while forming a protective barrier that reduces moisture loss when heat is applied to your hair shafts. Store bought heat protectants are generally made with a formula that includes the combination of two silicones – cyclomethicone and dimethicone. While cyclomethicone moisturizes your hair, dimethicone coats it, making it smooth and preventing moisture loss. They are generally safe.