When the Fantatsic Four go into combat they have specialist uniforms required for their mutation. Throughout the 2015 film there has been many different re-designs.
The team's uniforms are containment and beta suits, designed to stabilize and control each individual's mutation. Johnny's being made of fire-proof materials, Sue's being made of materials that can turn invisible with her, and Reed's being designed to keep him together. Ben is the only member who doesn't receive a uniform due to the extremity of his own mutation.