Conventional bathtubs come in a wide range of shapes, sizes and colors. There are freestanding models, such as old-fashioned clawfoot tubs or ultra-modern tubs resting on platforms, which can be placed in the middle of a large bathroom to create a dramatic appearance. Built-in tubs, on the other hand, may be modestly tucked into an alcove (walls on three sides), set in a corner or dropped into a frame (which usually allows more ledge room for storage of bath items or display of decorative items). Drop-in tubs can also be raised on a platform or recessed into the floor. Some are built for one person, others for more than one. Built-in tubs typically have one or two finished, external sides only --the sides that people will see -- while drop-in tubs have no finished exterior walls because the frame will conceal the sides of the tub (as the underside of a sink is covered by a cabinet). There are many manufacturers of conventional bathtubs. Kohler and American Standard are most commonly found in home-improvement stores, and prices range from a couple hundred dollars to well into the thousands depending on the size and the material used.
Conventional bathtubs may be made from any number of materials. Plastics are very common, inexpensive and don't get excessively cold. They're less prone to chipping than steel or cast-iron tubs coated with porcelain enamel, but plastic surfaces can scratch easily if you use abrasive cleaners or bathe a long-nailed pet in it. Most major bathtub manufacturers also offer some proprietary composites --for example, a combination of steel and resin that's more substantial-feeling than plastic yet lighter than cast iron, or a cast polymer that looks like marble or granite. Enamel-coated steel bathtubs are lighter and less expensive than enamel-coated cast iron, but they are more prone to chipping and they can be a bit noisy when you're running water to fill it. High-end designer freestanding tubs may also be made of metals like stainless steel or copper, sometimes double-walled to retain heat.
Freestanding tubs sometimes have more of a slope to the back (called a slipper tub), which can be more comfortable if you expect to take prolonged soaks. There are also dual clawfoot tubs that are rounded at both ends, with fixtures along one side and a center drain, so two people can bathe at the same time with reasonable comfort. A clawfoot certainly can add a retro charm to a bathroom, but not all of them can accommodate a shower. You sometimes can acquire an old one via salvage or antique dealer and have it reconditioned.
To maximize the longevity of a bathtub's finish, follow the manufacturer's recommendations on cleansers. Especially if you have an acrylic or fiberglass tub, you'll want to stay away from abrasive or harshly acidic cleaners.