A:A "Tile Flange" is a edge that is put on the outside of the tubs that will allow it to be installed up against a wall. Take a look at the secopnd page on the following .pdf: http://www.us.kohler.com/onlinecatalog/pdf/1003071_4.pdf On the right there is a small drawing that says "Tile Flange Detail", and it shows a small picture showing the extra edge they add. If you look at the picture below this, it shows the edge with out the extra flange added. If you are installing this as a "drop-in", where you build the surrounding structure and then "drop" the tub in through a hole in the top of the structure, then you do not need the tile flange option. If you are placing this against a wall, and then building the structure, then you will need to buy the flange version. This will seal the water from getting behind the tub where it touches the wall.