Fitting models range in age as well as size from petite to plus. Every type of clothing is fitted from ski wear, dresses, shoes, suites and lingerie. (Etc) A fitting model is normally well proportioned and required to maintain the same size. This is crucial for the development of the garment.
A fit model (person) is selected (to work as a fitting model) when their body measurement fit the criteria of the designer or manufacturer. These measurements can slightly vary from one company to another but are normally specifications consisting of height, bust-waist-hip circumference, bicep, thigh and shoulder width. This explains why some stores have clothes that fit you very well and others not as well.
Sometimes a model is required to present a collection of garments in a buyers meeting ahead of the production. This means that a company will be shown a collection/garment by a designer. The fitting model is asked to show the collection/garment, as the quality of the fit can be determined at this stage. A silk bra for example could be a beautiful fit on an A cup bra but on a F cup bra the fabric could be too rigged to lay flat over the larger cup.
This helps the buyer’s decision on whether to buy into that product or too change the fabric. A model can also aid in the development of the garment in preparation of the production line, by attending regular fitting sessions. When the garment is fitting perfectly it will receive the stamp of approval sent to the factory for production and then into the stores where the consumer can purchase the perfect fitting item.