Vitrified tiles are often used outdoors due to their water and frost resistance.
There are four types of Vitrified tiles - Soluble salt, Double charge, Full Body, and Glazed.
Vitrified tile is made by hydraulic pressing a mixture of clay, quartz, feldspar and silica, which make vitreous surface.
Thus creating a single mass making them hard with low porosity.
Different clay bodies reach vitrification at different temperatures.