There is a slight difference between thermal and anti-fog lenses. To understand this, it is important to know that a thermal lens is relatively more extensive than an anti-fog lens. The anti-fog lenses are basically designed to protect your mask from building up the excessive fog. On the contrary, the thermal lens is a two-fold lens that allows airflow and shares the trapped air through ventilation and prevents fogging. Similarly, thermal lenses are dual-pane lenses designed for both inner and outer lenses that surround the edge of the mask and prevent the air from getting trapped in. For instance, the outer lens is designed big and dense so that it protects your mask from external air. Whereas the inner length is light that works similar to a dual-pane design that adds to the protection and prevents any chance of fogging. Hence, if you want to protect your lens a step further, having a thermal lens can help you ideally.