The problem with pressure bandages, which are used to treat medical issues around veins that don’t return enough blood from your legs or arms, is that there’s no way to know if the pressure being applied is optimal for the specific condition. Engineers have found a way to solve this problem by developing color-changing fibers that can be woven into pressure bandages and change color according to how much the bandage is stretched. Once a caregiver has stretched a patient’s bandages enough to apply a certain amount of pressure, the color-changing fibers can be used as a visual check on the amount of pressure the bandage is providing.