The 3-wall alcove tub is the most commonly used tub. It is installed into a recess with walls on both ends and one side. The remaining side is referred to as the “skirt” or “apron”. These tubs tend to be 5-6 feet long.
The 3-wall alcove tub used to be made solely out of cast iron; however, they are now made from other metals, porcelain, acrylic or fibreglass. Fibreglass is the cheapest and damages easily. Often, replacing a fibreglass tub makes more sense than reglazing. This is not the case for the others.
The corner tub is designed to fit in the corner of the bathroom. Many are five-sided with a triangular basin, designed for two people to bathe at the same time. They tend to be made out of acrylic or fibreglass.
A Drop-in bathtub, which has a finished rim, is designed to be “dropped” into a deck or custom surround. These tubs can be installed in corners, islands or sunk into the floor. These tubs are supported from below, as well as above, as the finished rim sits over the frame. These tubs tend to be large, like the corner tub and are usually made out of acrylic or fibreglass.
An under-mount tub is installed under a solid surface deck and therefore gives the illusion that the deck and the tub are all one piece. Like the corner tubs and drop-ins, the under-mount tubs are made out of acrylic or fibreglass.
The corner, drop-in and under-mount bathtubs are the classic soaker tubs as they are large and often come with built in hand rests. Many manufactures have started to make a 3-wall alcove soaker tub, which is bigger than the standard 3-wall alcove tub, but smaller than the corner/drop-in and under-mount. All of these tubs can be found with Jacuzzi jets, turning your soak into a bubbly experience.
Lastly, the freestanding or claw foot tub is the old style, deep, elegant tub of yesterday! It is almost always installed away from the wall, often sitting in the middle of the room. They used to be made solely out of cast iron, as they retain heat very well. Now they can be found in metal, acrylic or even fibreglass. There are many different types of feet and fixtures that can be installed on the claw foot’s making them as personal as you like.
Much of the above information was taken from the following site: http://www.us.kohler.com/onlinecatalog/buyguide/baths1.jsp
Pictures were taken from Google Images