I dont understand what they are, can some one explain, thanks!

 

Please?

 

its like having a gas tank in your trunk...used in race cars, also with cars that run race fuel in their street cars...they have a small fuel cell that just holds race fuel

 

so its just a gas tank in the trunk

 

Commonly, they have a foam/sponge core within. This limits the amount of fuel that can be immediately dumped in the event that the fuel-cell is ruptured during an impact. Such a core also limits the sloshing of fuel during transitions.