Flexible Supply Lines Under Sink: Braided vs. Corrugated — Which Should You Buy?

When you’re replacing a faucet or toilet and need to pick up new flexible supply lines for under-sink connections, the hardware store aisle can be more confusing than it looks. Two main types exist — braided stainless steel and corrugated metal — and they’re not interchangeable in every situation. This article breaks down the real differences so you can grab the right flexible supply lines for under sink use before you get on your knees and open the cabinet.

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What Flexible Supply Lines Do Under Your Sink

A supply line does one job: it connects the shutoff valve on the wall or floor to the inlet on your faucet, toilet fill valve, or appliance. The flexibility is the point — a rigid pipe connection under a sink would crack under the minor vibration, movement, or installation angle mismatches that are completely normal in a cabinet space.

Each supply line has two ends. The valve end typically uses a compression fitting or threaded connection that seats onto the shutoff valve outlet. The fixture end uses a threaded fitting that screws into the faucet inlet or fill valve.

Standard sizing for most U.S. homes: 3/8″ at the valve end, 1/2″ at the fixture end. Measure both before you buy. Length matters too — 12″ for tight spaces, 20″ for most standard under-sink configurations, and 24″ for deep cabinets or offset placements.

Braided Stainless Supply Lines: Strengths, Weaknesses, and Best Uses

Braided stainless supply lines are the current standard for residential plumbing. The construction is a polymer inner tube — usually PVC or EPDM, a synthetic rubber — wrapped in a woven stainless steel mesh jacket. That outer mesh is what gives them their name and most of their strength.

Strengths

• High burst pressure resistance — the stainless mesh significantly reinforces the inner tube against pressure spikes
• Kink-resistant — holds its shape after installation without fatiguing at bend points
• Clean appearance — modern and unobtrusive in an under-sink cabinet
• Widely available — every hardware store and home center carries them in standard lengths
• Standard fittings — most come pre-fitted with the 3/8″ compression x 1/2″ FIP (female iron pipe) combination that fits the majority of residential shutoff valves

Weaknesses

• The inner tube degrades over time even when the exterior looks intact. Most manufacturers rate braided lines at 5–8 years — the stainless jacket hides any deterioration until the line fails
• Overtightening crushes the rubber or nylon seat inside the fitting, which causes leaks rather than stopping them
• Slightly less forgiving if the connection angle requires a very sharp bend right at the valve end

Best Uses

Braided stainless is the right choice for almost every standard faucet replacement, toilet fill valve connection, and dishwasher inlet connections. It’s the default recommendation whenever someone asks which flexible supply line to buy under the sink. For most homeowners, the decision starts and ends here.

A set of 3/8″ compression x 1/2″ FIP braided stainless supply lines in a standard 20″ length covers the majority of under-sink faucet and toilet installs.

Corrugated Supply Lines: When the Old Standard Still Makes Sense

Corrugated supply lines are the older technology — soft copper or chrome-plated brass tubing that’s accordion-crimped along its length to allow bending without separate fittings. They were the residential standard before braided lines became widely available, and they still show up in older homes.

Strengths

• High routing flexibility — you can hand-bend a corrugated line around obstacles and hold unusual angles that a braided line can’t manage as easily
• No inner tube to degrade — the metal itself carries the water; there’s no hidden polymer layer wearing out behind an intact-looking exterior
• Solid fittings — no separate compression ring needed in most cases; the fittings are integral to the tube
• Can be cut to a custom length with a tube cutter, which is useful in retrofit situations

Weaknesses

• Kink-prone — if bent too sharply or repositioned repeatedly, the accordion folds can flatten and restrict flow or crack
• Fatigue cracking — pinhole cracks can develop at bend points over time, especially in high-vibration environments
• Harder to find — most modern hardware stores carry limited corrugated stock; you may need a plumbing supply house
• Chrome-plated versions can corrode once the plating is compromised

If you’re working with corrugated copper and need to cut a line to a custom length, a small tube cutter is the right tool for a clean, square cut.

Best Uses

Corrugated lines still make sense in tight spaces where a rigid angle is unavoidable, in older homes where the existing connections are corrugated, or in retrofit installs where matching the original connection style is the cleanest approach. They’re not inferior — just more situational.

Braided vs. Corrugated Flexible Supply Lines: Side-by-Side Comparison

For most homeowners, braided stainless wins on durability, availability, and ease of installation. Corrugated earns its place in situations where unusual routing angles make flexible bending a practical necessity — not as a general-purpose upgrade. Either way, both types of flexible supply lines under sink cabinets will outlast a sloppy installation, so technique matters as much as type.

How to Choose Flexible Supply Lines for Under-Sink Connections

Here’s the decision tree for picking the best supply lines for a faucet or toilet connection:

• Replacing a standard faucet or toilet supply line? → Braided stainless is the default. Buy the correct length and standard 3/8″ x 1/2″ fittings and you’re done.
• Routing around a deep cabinet corner or unusual valve placement? → Corrugated gives you more bend control without kinking — use it here.
• The existing line is corrugated and fits perfectly? → Corrugated replacement is acceptable, but inspect the old line’s bend points before assuming the same routing still works. If there are flat spots or visible cracks, reroute.

Getting the Length Right

Measure from the center of the shutoff valve outlet to the fixture inlet, then add 2–3 inches of slack. Never stretch a supply line taut — a taut line stresses both fittings and is one vibration away from a drip. A little extra loop is fine; a straight, tight line is not.

Fitting Types

At the shutoff valve end, most residential valves use a 3/8″ compression fitting. Braided lines come with this pre-installed — no extra parts needed. Push-fit (SharkBite-style) valve ends also exist but are less common on supply lines specifically. Confirm your valve type before buying.

At every threaded connection, use PTFE pipe tape — also called thread tape or plumber’s tape. Wrap the male threads 2–3 times before threading on the fitting. This seals the connection and prevents slow weeping leaks at the threads. Good quality PTFE pipe tape is inexpensive and worth keeping under the sink for any future work.

Installing and Tightening Flexible Supply Lines Under Sink Cabinets Without Causing a Leak

This isn’t a full installation guide, but these steps cover the most common mistakes — including the ones that cause a brand-new line to drip on day one.

1. Shut off the supply at the shutoff valve under the sink. Turn it clockwise until it stops. If the valve won’t close fully or is leaking around the stem, stop here — the supply line swap is not the right starting point. The shutoff valve needs replacement first.

1. Hand-thread both fittings — valve end first, then fixture end. Never start with a wrench. If it won’t thread on by hand, something is misaligned or cross-threaded.

1. Snug with a wrench. For braided lines at the fixture end (faucet or fill valve), no more than 1/4 turn past hand-tight is typically enough. The compression fitting at the valve end needs firmer tightening — use steady pressure, not force.

1. Turn the water back on slowly and watch both ends for 60 seconds. A slow drip is easier to catch now than after the cabinet door is closed.

1. If a drip appears at a threaded connection, turn off the water, remove the fitting, apply PTFE tape to the male threads, and retighten. Do not simply crank harder on a dry threaded connection — that damages the seat.

The overtightening warning is real. Braided stainless lines have a rubber or nylon washer inside the fitting. Crush it by overtightening and the seal gets worse, not better. Hand-tight plus a quarter turn is almost always enough.

For faucet supply line connections specifically, the nuts sit up against the underside of the sink deck and are nearly impossible to reach with standard pliers. A basin wrench — a long-handled tool with a pivoting jaw designed for exactly this position — makes the job dramatically easier. Without one, you’re fighting the geometry of the cabinet every time.

Which Flexible Supply Lines Under Sink Should You Buy?

For 90% of homeowners replacing a faucet, toilet, or appliance supply line, braided stainless is the right call. It’s available everywhere, rated for both hot and cold supply lines, DIY-friendly, and priced so low that there’s no reason to reuse an old line when you’re already doing the work.

Go with corrugated only if your installation genuinely requires it — unusual angles, tight retrofit spaces, or matching existing corrugated connections in an older home.

Whatever type you choose: use PTFE tape at the threads, don’t overtighten, add a couple inches of slack, and replace both lines anytime you’re replacing the faucet or shutoff valve regardless of how old the existing lines look. The lines are cheap. Water damage from a failed supply line inside a closed cabinet is not.

Frequently Asked Questions

How often should flexible supply lines be replaced? Braided stainless lines are typically rated for 5–8 years. Corrugated lines should be inspected at 5 years for kinks, flat spots, or corrosion. Replace both types whenever you replace the faucet or shutoff valve — don’t reuse old lines just because they look intact.

Can I reuse my old supply line when replacing a faucet? Technically possible if the length and fittings match, but not recommended. Supply lines are inexpensive, and a fatigued line carrying water in an enclosed cabinet is a slow water damage risk waiting to happen.

Why is my new supply line dripping at the fitting after tightening? The most likely cause is a missing or displaced washer inside the fitting, or overtightening that crushed the seat. Remove the fitting, inspect the washer, replace it if deformed, and hand-thread carefully before snugging with a wrench.

What length supply line do I need? Measure from the valve center to the fixture inlet and add 2–3 inches. A 12″ line fits tight spaces, 20″ fits most standard under-sink configurations, and 24″ works for deep cabinets or offset placements.

Is braided stainless safe for hot water lines? Yes. Quality braided stainless supply lines are rated for both hot and cold connections. Most EPDM-lined braided supply lines are rated to 180°F, which comfortably covers residential hot water supply temperatures. The inner tube handles normal household water temperatures without degradation.

Mike Torrance

DIY Home Repair & Plumbing

Mike has spent 20 years fixing things around his own home. From leaky pipes to patching drywall, he writes about what actually works for homeowners who want to handle repairs themselves.