The tube has two separated channels, or lumens, running down its length. One lumen, open at both ends, drains urine into a collection bag. The other has a valve on the outside end and connects to a balloon at the inside tip. The balloon is inflated with sterile water when it lies inside the bladder to stop it from slipping out. Manufacturers usually produce Foley catheters using silicone or coated natural latex. Coatings include polytetrafluoroethylene, hydrogel, or a silicon elastomer – the different properties of these surface coatings determine whether the catheter is suitable for 28-day or 3-month indwelling duration.