Rather than wearing the cheesy suits we normally associate with the superhero group, this Fantastic Four will wear something a little different, as Michael B. Jordan (Johnny Storm) explained in a recent interview:
It's a new look. We are all in containment suits. It's gritty. It's a gritty film. The costume process definitely took some time to get in and out of that thing, especially since I was bulking up. It was a little more snug during filming. We got through it man. It was a process, but we did it. It was hard work. I'm really excited about it, everyone is really happy. We worked hard for three months, put a lot of time into it. The script is very grounded and relatable to everybody, as much as you can. You really get a chance to grow with these characters. It's an origin story. You get to discover these abilities. These disabilities rather and grow with them.
So, it sounds as though the group's powers need "containing", which suggests they might be somewhat unstable, and it is assumed the suits will be a Reed Richards creation. It'll certainly be interesting to see how they look.