A film’s emulsion type refers to the composition of its emulsion, whether it was manufactured to be fast, slow, grainy, fine-grained, colorful, pastel, black and white or color, daylight balanced, tungsten balanced, etc. The emulsion type is represented by a number. For Kodak it is a series of four numbers, such as 7248. The “72” always stands for 16mm camera stock, and the same emulsion type is found in 35mm as 5248, “52” being the designation of 35mm. Fuji uses a system where the film’s emulsion type is a little more telling, such as 250D, which is daylight balanced film with an exposure index of 250. When picking out a stock to use the film speed, and in the case of color film, whether the film is daylight or tungsten, are the primary reasons for choosing a certain emulsion type. Allowances might also be made to achieve a certain look, as in using Kodak Vision, or Fuji film. Several different emulsion types are usually used on a project, fast for night scenes, slow for daylight scenes, etc. However, unless you are trying something novel, it is a good idea to shoot a single unbroken sequence with one emulsion type.
Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/
reprinted with permission