Porosity
When referring to porosity there are four types of tile. Impervious tile has less than .5 percent absorption and is frost proof. Vitreous tile absorbs less than 3 percent moisture and can be used indoors and out. Semi vitreous tiles absorb somewhere between 3 percent and 7 percent moisture and are suitable in certain indoor applications. Non-vitreous indicates a product that absorbs 7 percent or more moisture and cannot be used outdoors or in damp areas.
Porcelain
Porcelain is ceramic tile that is composed of finer clay and materials that are fired at high temperatures. This makes it harder and more durable than other tiles. Porcelain is more scratch- and stain-resistant than other tiles, and the color goes all the way through, making chips less noticeable.
Tile Density
The high-firing temperature for porcelain makes it a denser, stronger product, which in turn makes it less absorbent. Tile density is an important factor to consider when choosing tile.
Application
Though semi vitreous tiles are fairly durable, they are suitable only for indoor applications because they absorb some moisture. They should be used in an area that will not be exposed to significant moisture, but they can tolerate some contact with water. A backsplash is a common place to use semi vitreous tile.
Sealants
Because semi vitreous tiles absorb more water than vitreous tiles, they may need to be sealed if you want to use them in damp rooms like bathrooms. Sealants could alter the color of the tile, so it is a good idea to test the sealant on the tile before you decide.