Pre-slit foam tubes are a practical starting point for exposed water pipes in unheated spaces. Match the cover to the pipe diameter and close gaps at joints. Insulation slows heat loss; it cannot guarantee freeze protection. If a run needs a heating cable, check the exact pipe material, installation location and cable instructions before buying.
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Our pick: Duck Brand pre-slit foam pipe covers for 1/2-inch to 3/4-inch pipe. Check the Duck Brand foam pipe covers on Amazon
A frozen pipe that splits can flood a house, and it is worse when the split is inside a wall, because it usually starts leaking only when the ice thaws. The prevention takes an afternoon, and the time to do it is before the first hard freeze.
| Product | Best For |
|---|---|
| Duck Brand Pre-Slit Foam Pipe Covers | Best Overall |
| Frost King FV15 Foam and Foil Pipe Wrap | Best for Irregular Shapes |
| Frost King HC Automatic Heat Cable Kit | Best for Extreme Cold |
Best OverallEditor’s Choice
Duck Brand Pre-Slit Foam Pipe Covers
foam tube · pre-slit with self-sealing edges · fits 1/2 in to 3/4 in pipe · R-value 3.6 (per the listing) · rated to 212°F · six 12-inch sticks per pack (6 ft) · made in the USA
Check the Duck Brand foam pipe covers on Amazon →
Pre-slit foam tube is the standard for pipes in unheated spaces — crawl spaces, garages, basements and attics. This Duck Brand pack opens along a pre-cut seam, slips over the pipe, and the listing says the edges are self-sealing, so there is no separate tape job on the seam. The listing gives it for both hot and cold water pipes, an R-value of 3.6, a temperature rating of 212°F, and a fit of 1/2-inch to 3/4-inch pipe — the two sizes that make up most of a house’s water lines.
The catch is the stick length. Each piece is 12 inches, six to a pack, so a 20-foot crawl-space run takes four packs and leaves a butt joint every foot. Those joints are where insulated pipes still freeze, so press every one tight and wrap it with foam tape (the next pick) where it meets an elbow or a valve.
- Pre-slit with self-sealing edges, so it goes on without cutting or taping the seam.
- The listing rates it for hot and cold lines up to 212°F and gives an R-value of 3.6.
- Fits 1/2 in to 3/4 in pipe, the sizes most homes run for water supply.
- Sticks are only 12 inches long, so long runs need several packs and have a joint every foot.
- Sized for 1/2 in to 3/4 in pipe only; a 1 in main needs a different tube.
Verdict: Best for straight copper, PEX or CPVC runs in a crawl space, garage or basement where a slip-on tube saves the most time.
Best for Irregular Shapes
Frost King FV15 Foam and Foil Pipe Wrap
self-adhesive foam tape with a foil face · 2 in wide × 1/8 in thick × 15 ft roll · for hot and cold pipes · made in the USA
Check the Frost King FV15 foam-and-foil wrap on Amazon →
For valves, tees, elbows and the short stubs where a tube will not sit, a self-adhesive tape fills in the coverage. The listing describes this Frost King roll as a self-adhesive foil-and-foam tape for hot and cold pipes: on hot lines it cuts heat loss, on cold lines it stops sweating. Wrap it spiral-fashion with a half overlap, and use it to seal the butt joints between foam sticks.
At 1/8 inch thick it is a supplement, not a primary barrier. On a long exposed run, the tube does the insulating and the tape closes the gaps.
- Self-adhesive, so it stays put on elbows, tees and valve bodies without extra tape.
- Foil face plus foam, rated by the listing for both hot and cold pipes.
- A 15 ft roll covers a lot of fittings and the seams between foam sticks.
- At 1/8 in thick it adds far less insulation than a tube on a long straight run.
- Wrapping fittings by hand takes longer than sliding on a pre-slit tube.
Verdict: Best for sealing the fittings, valves and tube joints that rigid pipe insulation leaves exposed.
Best for Extreme Cold
Frost King HC Automatic Heat Cable Kit
120V plug-in pipe heating cable · 7 W/ft · keeps water flowing down to −40°F (per the listing) · for metal and plastic water pipes · sold in fixed lengths (Frost King lists kits from 3 ft to 30 ft, HC3A to HC30A) · the listing linked here is the 6 ft HC6A
Check the Frost King HC6A heat cable on Amazon →
A heating cable adds heat where insulation alone cannot keep a water-filled supply pipe warm. The linked HC6A is a fixed-length, six-foot cable; do not cut it to fit. Frost King’s HC installation instructions (frostking.com) exclude drain lines, fuel lines, hoses and buried installations, and call for the finished job to be wrapped in 1/2 inch fiberglass insulation and never more than that, warning that over-insulation can make the cable overheat and cause a serious fire hazard or electrical shock.
They also say to run the cable straight along the pipe, never wrapped or spiraled, never to let it touch, cross or overlap itself at any point, never to use a cable longer than the pipe, and never to install it on plastic pipe unless the pipe is filled with water at all times. Its product FAQ (frostking.com) also excludes mobile-home feed lines and installations enclosed in walls, floors or ceilings. Check those limits before selecting this kit.
Two rules from the U.S. Consumer Product Safety Commission belong here, because they change how the insulation above is used. CPSC says to put a heat tape directly on the pipe, never on top of the insulation, to plug it into a GFCI-protected outlet, and not to cover it with foam or vinyl insulation that could catch fire if the tape fails; where the manufacturer allows a cover, CPSC advises a non-flammable one such as fiberglass.
So on the section you heat, the foam tubes above come off and the cable maker’s instructions decide the covering. We compare cable types in our heat tape guide.
- The listing rates it to keep water flowing down to −40°F, far past what passive foam can do.
- Made for metal and plastic water pipes, per the listing.
- Sold in fixed lengths from 3 ft, so a short problem section does not need a long cable.
- Needs a grounded, GFCI-protected outlet within reach (CPSC guidance).
- Not a foam-covered install: CPSC advises against covering heat tape with foam or vinyl insulation.
- It stops working in a power outage, which is often when the cold is worst.
Verdict: Best for the one section that freezes every winter, once you have an outlet nearby and have read the cable’s own instructions.
What Is the Best Pipe Insulation for Freezing Temperatures?
Closed-cell polyethylene foam handles most freezing weather — it is the standard for crawl spaces, garages, basements and attics, and it is sold pre-slit in the common pipe sizes. Where an exposed pipe has frozen before, foam alone is not enough; that section wants a heat cable. A pipe hidden inside an exterior wall is different: heat tape there cannot get the yearly inspection CPSC calls for, so keep the heat on and let the cold tap drip in very cold weather (American Red Cross), and have a plumber look at rerouting or insulating that run.
Understand what the foam is doing: it reduces heat loss, so it prevents freezing only for as long as the pipe still has heat to lose. At extreme temperatures, or on a run with no warmth behind it, the cable is what keeps the water liquid — and the cable changes the covering, because CPSC advises against foam or vinyl insulation over heat tape.
Which Pipes Should You Insulate for Cold Weather?
Both hot- and cold-water supply pipes can freeze when the surrounding space gets cold enough. A hot-water line cools between uses; do not leave it unprotected because it normally carries hot water. The American Red Cross recommends insulating both (redcross.org).
The American Red Cross lists the same trouble spots: outdoor hose bibs, supply pipes in unheated basements, crawl spaces, attics, garages and kitchen cabinets, and pipes against exterior walls with little or no insulation. It also says both the hot and cold pipes in those areas should be insulated.
Foam or Fiberglass Pipe Insulation: Which Is Better?
Foam for cold runs and ordinary hot-water lines; fiberglass where the pipe runs hot. Fiberglass is also the non-flammable cover CPSC names for use over heat tape where the cable maker allows one. For freeze protection in a crawl space, the foam tube installs faster and will not shed particles.
Comparing rubber and polyethylene tubes? Our rubber-versus-foam insulation comparison explains exact formulations, temperature limits, thickness and the difference between thermal-conductivity figures and installed R-values. Check the complete covering system rather than choosing by material name alone.
PEX Pipe Insulation: What Size Fits PEX?
PEX takes the same foam as copper. PEX tubing is sized to copper tube size (CTS), so 1/2-inch PEX has a 0.625-inch (5/8-inch) outside diameter, the same as 1/2-inch copper, and 3/4-inch PEX is 0.875 inch, the same as 3/4-inch copper (PEX tubing dimensions, PexUniverse (pexuniverse.com)). Buy foam labeled for 1/2-inch or 3/4-inch copper or PEX. The Duck Brand covers above are listed for 1/2-inch to 3/4-inch pipe; the listing does not name PEX, so check that the tube closes snugly on your line.
The size to avoid is iron pipe size. Half-inch iron pipe measures 0.84 inch across the outside (Hayes IPS pipe size chart (hayesfusion.com)), about a third bigger than 1/2-inch PEX, so foam sized for iron pipe sits loose on PEX and leaves an air gap along the run.
PEX water lines in cold spaces also benefit from insulation. If you are considering a heating cable, check both the cable instructions and the exact PEX manufacturer’s guidance. A listing that says “plastic pipe” is not enough to establish compatibility with every plastic material or installation. Frost King’s current product information describes plastic supply pipes generally but separately excludes PVC in its FAQ; resolve the exact pipe-and-cable combination before buying or installing it.
FAQ
How do I know what diameter foam to buy?
Measure the outside diameter of your pipe. Most residential 1/2″ copper pipe has a 5/8″ OD — buy foam labeled for 1/2″ copper. 3/4″ copper has a 7/8″ OD. Pipe insulation is labeled by nominal pipe size, so just match the nominal size.
My pipes still froze after insulating. What went wrong?
Either the foam had gaps at joints and fittings, the temperature dropped below what foam alone can handle, or the pipe is in an exterior wall without any interior heat source nearby. For an exposed section that keeps freezing, add a heat cable and follow the cable maker’s instructions on what may cover it. For a pipe inside an exterior wall, let the cold tap drip in very cold weather (American Red Cross) and have a plumber look at rerouting it.
When should I insulate my pipes?
Before the first freeze where you live. Any time of year works; the foam goes on in an afternoon.
What size pipe insulation fits 1/2-inch PEX?
The size for 1/2-inch copper. PEX is made to copper tube size, so 1/2-inch PEX has a 0.625-inch (5/8-inch) outside diameter, the same as 1/2-inch copper, and 3/4-inch PEX matches 3/4-inch copper at 0.875 inch. Foam sized for 1/2-inch iron pipe, which is 0.84 inch across, is too loose.
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Pre-slit foam covers most pipes in most climates, copper or PEX, with foam tape on the fittings and joints. For an exposed section that freezes anyway, put a heat cable on it and cover it the way the cable maker and CPSC say, not with foam. A few hours of work is far less trouble than a burst pipe.
Going away for part of the winter? A freeze alarm texts you when the house gets cold, before a pipe does. And if a spigot is the weak point, the permanent fix is a frost-free sillcock; the full cold-weather list is in our winterizing checklist.
Already frozen? Insulation is prevention — if a pipe is frozen now, see how to thaw frozen pipes.
Not sure where a cover or insulation fits in the bigger picture? Follow the full 15-minute outdoor faucet winterization checklist before the first hard freeze.