There are three main materials baths are made from: Cast-iron, Pressed steel and plastic/Acrylic.
We can resurface all of these.
CAST IRON BATHS. Cast iron is what baths have traditionally been made from. Baths have been made this way for a long time so you come across many different styles from Victorian roll-top baths with clawed feet, 1930′s art-deco style with broad, square shoulders and boxed in with cast-iron panels in matching colour (the most common colour of these baths is green/avocado) through to the much plainer baths of the fifties and sixties which are boxed in with panels made from ply or the like. Then as you get into the 70′s and 80′s you come across baths where the enamel is coloured, the baths often have handles and again, usually the are boxed in. The baths themselves are heavy. They do not flex when you get in them.
PRESSED STEEL BATHS. These baths are quite common today and are often still used in new-build houses. Generally look very similar to cast iron baths from the fifties and sixties but are much thinner and lighter. If you rap them with your knuckle you can hear a “ring” from a pressed-steel bath which you won’t get from a cast-iron bath. Usually boxed-in.
PLASTIC/ACRYLIC BATHS. Very common from the seventies through to the present. A lot of the bathroom suites you see with strong colours such as burgundy, blue, mustard, green and so on tend to (but no always) have plastic baths. Also tend to come in a wider variation of shapes than the cast or pressed steel baths.
These baths flex more when you use them and have a layer of plywood or chipboard under the base of them to stiffen and add strength.
A modern trend with plastic baths is to make them from much thicker material so they don’t flex and to do them in a roll-top style and not boxed in, so you see the outside and feet of the bath.