A Foley catheter is a flexible tube inserted through the urethra into the bladder, where a small inflatable balloon holds it in place so urine drains continuously into a collection bag. The system relies on gravity, not suction or pumps, which is why the drainage bag always hangs below the level of your bladder. Understanding how each part of this device works can make the experience far less intimidating if you or someone you care for needs one.
The Three-Channel Design
A Foley catheter looks like a single tube from the outside, but it actually contains two or three separate internal channels (called lumens) running its full length. The largest lumen is the drainage channel, allowing urine to flow from the bladder down into the collection bag. A second, much narrower channel connects to a small balloon near the catheter tip. This is the retention balloon, and it’s what makes a Foley catheter different from a simple straight catheter that would slide right back out.
Some catheters have a third channel used for irrigation, flushing fluid into the bladder when needed. But the standard two-channel version is by far the most common.
How the Retention Balloon Works
The balloon sits deflated and flat against the catheter tip during insertion. Once the tip is confirmed to be inside the bladder, sterile water is injected through the inflation channel, typically about 10 cc (roughly two teaspoons). The balloon expands into a sphere that’s too large to slip back through the bladder neck, anchoring the catheter in place without stitches or tape inside the body.
Getting the inflation right matters. An underfilled balloon won’t form a proper sphere, and an irregularly shaped balloon can allow the catheter to dislodge. Sterile water is preferred over saline for inflation because saline can form tiny crystals inside the balloon over time, which may interfere with deflation later. This is especially relevant for catheters that stay in place for weeks.
After inflation, the catheter should still move slightly when gently pushed. If it feels completely stuck, the balloon may have inflated in the wrong location, such as the urethra rather than the bladder.
Gravity Does the Work
Once the catheter is in place, urine flows through the drainage lumen and down the tubing into a collection bag. No mechanical force is involved. The system depends entirely on gravity: urine in the bladder sits higher than the bag, so hydrostatic pressure moves it downward through the tube.
This is why bag positioning is critical. The collection bag must always hang below bladder level. If the bag rises above the bladder, or if the tubing kinks or loops upward, urine can stall or even flow backward, which significantly raises the risk of urinary tract infection. In some cases, placing the bag in a basin on the floor is recommended to ensure adequate gravity flow. The bag should be emptied when it’s about two-thirds full to prevent backflow from the weight of accumulated urine.
Catheter Materials and Sizing
Most Foley catheters are made from either latex or silicone. Silicone catheters resist kinking better and have superior flow properties compared to latex-based options. They’re also the go-to choice for anyone with a latex allergy, which is common enough in both patients and healthcare workers that many hospitals have shifted toward silicone as the default.
Catheters are measured using the French scale, where each French unit equals one-third of a millimeter in outer diameter. A 16 French catheter, one of the most common adult sizes, is about 5.3 mm across. Smaller sizes are used for children, and larger sizes may be needed when urine contains blood clots or debris that could block a narrower tube. The goal is always to use the smallest size that drains effectively, since a larger catheter puts more pressure on the urethral lining.
What Insertion Feels Like
Before insertion, the area around the urethral opening is cleaned with an antiseptic solution, and a sterile lubricant (often containing a numbing agent) is applied. The catheter is then gently advanced through the urethra. In women, the urethra is only about 4 cm long, so the catheter reaches the bladder quickly. In men, the urethra is roughly 20 cm and curves through the prostate, so insertion takes a bit longer and may involve more pressure.
Most people describe the sensation as uncomfortable pressure rather than sharp pain. You may feel a strong urge to urinate as the catheter passes through the urethra, which is normal. Once the balloon is inflated inside the bladder, you’ll typically feel a mild tugging sensation if the catheter shifts, but the discomfort usually fades within minutes to hours as your body adjusts.
How Long a Catheter Stays In
There’s no universal expiration date for a Foley catheter. The CDC specifically recommends against changing catheters on a fixed schedule. Instead, replacement should happen based on clinical need: signs of infection, blockage, or a break in the closed drainage system. Some catheters stay in for just a few hours after surgery, while others remain for weeks or longer in people with chronic urinary retention.
The overriding principle in hospitals is to remove the catheter as soon as it’s no longer necessary. Every extra day increases infection risk. Many hospitals now use nurse-led daily review protocols, where staff check each day whether a patient’s catheter still has a valid reason to stay in place. Catheters inserted in emergencies, where sterile technique may have been compromised, are typically replaced or removed within 24 hours.
How Removal Works
Removing a Foley catheter is simpler and faster than putting one in. A syringe is attached to the balloon inflation port, and the sterile water is drawn back out, collapsing the balloon. Once deflated, the catheter slides out through the urethra with gentle traction. The whole process takes seconds.
Afterward, you may feel a brief burning sensation when you first urinate on your own. Some people experience temporary difficulty starting their urine stream or feel urgency and frequency for a day or two as the bladder readjusts to filling and emptying on its own. This is normal. The urethra may also feel mildly irritated for 24 to 48 hours. If a catheter has been in place for a long time, your bladder muscle may need a short period to regain its normal tone and coordination, but for most people, normal urination returns quickly.