Non -vitreous Tiles
These type of tiles absorb 7% or more of its body weight in water. They are suited for indoor use only and considered to be non-frost resistant.
Semi -vitreous Tiles
Absorb between 3% to 7% of its body weight in water. Also suited for indoor use only and considered to be non-frost resistant.
Vitreous Tiles
Absorb between 0.5% to 3% of its body weight in water. They are suited for both interior and exterior applications provided that the area is covered and/or non-heated rooms not exposed to standing water. They are also considered to be frost resistant.
Impervious Tiles
These tiles are the strongest. They absorb between 0 and 0.5% of their weight in water. Suited for both interior and exterior use and considered to be frost resistant. (NOT FREEZE PROOF).
One must also be aware of the C.O.F. (stands for coefficient of friction and means the slip resistance factor) when deciding on the use of these types of products in exterior applications.
WHITE BODY VS. RED BODY
This refers to the colour of the clay body used when producing glazed tile. Many distributors in the industry and consumers believe that one colour is superior to the other, but this is not necessarily true.
The quality of the tile has more to do with the quality of the manufacturer, density of the clay, and breaking strength rather than the colour of the clay. Porcelain is simply a finer grade of clay and makes a denser, harder tile body.
If the glaze was to chip from the white body, once the floor is mopped and water penetrates the body, you will be left with a brown spot. A red bodied tile would also brown after mopping, which makes any argument over the colour of the biscuit body pointless.
Source: http://www.homeresourceguide.com/Article-Ceramic.html
