This type is also sometimes known as the three-wall alcove bath and has become a popular choice mainly because of its affordability, space efficiency, and availability. Only the front part of the bath features any decorative finish since the alcove walls will conceal the other sides. You will usually find these type of baths made of Acrylic.
Some are also made of enameled steel, which is an inexpensive material and known to be relatively lightweight. However, the main downside of steel enamel is its tendency to create noise and prone to chipping after long use.
Another alternative to this is the enameled cast iron, which comes significantly more expensive and heavy that might require your bathroom floor additional reinforcements to support the extra weight