Help with dynamics (elasticity - tension)

Hi guys,

im trying to develop a car seatbelt (a safety belt) for a educational project…it consists on the user grabbing the seat belt and buckling it…

i tried my best but i cant get it to work properly…i need the belt itself to show some elasticity, tension, as the user moves it to buckle up…not just a black line getting bigger in the direction i want…

hope i could make myself clear…any help would be much much much very appreciated…

thanks in advance