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Does PEX Need To Be Insulated? Is It Worth Insulating PEX Pipes?

PEX or cross-linked polyethylene is a flexible plastic piping predominantly used in water supply lines. One of the main benefits of this piping is its ability to expand when frozen without breaking.

With this feature, you might wonder, does PEX need to be insulated after all? Yes, PEX must be insulated if the pipes are exposed and installed outside or inside unheated places like the basement. Typically, insulation is critical, especially if you live in an area with cold winters. However, insulation is not necessary if the PEX exists within insulated external walls or interior walls.

So then, what is the best insulation material for PEX pipe? Stick around to learn more about PEX insulation, including how to insulate the pipes.

Does PEX Need To Be Insulated?

Yes, especially if you live in areas with cold winters. However, if the PEX piping passes through insulated exterior or interior walls, it does not need insulation.

This is because PEX is highly resilient against temperature fluctuations compared to other plumbing materials like copper pipes. In fact, it can withstand temperatures as low as -40 degrees Fahrenheit and as high as 200 degrees F.

When Is It Necessary To Insulate PEX?

Typically, PEX needs to be insulated if exposed and installed in uninsulated areas, such as:

  • Basements
  • Crawl spaces
  • The Attic
  • Exterior walls

This is because while PEX can withstand extreme temperatures, the pipes would freeze if the temperatures reach 20 degrees F or below. As a result, the piping would expand due to ice formation, causing them to break or burst. After all, PEX is only freeze-resistant but not freeze-proof.

Benefits of Insulating PEX

Insulating PEX helps the pipes retain heat even during those cold winters. Other benefits of insulating these pipes include the following:

1. Promoting Energy Efficiency

Insulating PEX helps reduce heat loss through the walls, ensuring maximum energy efficiency. Simply, the insulation ensures the hot water stays hot even when the temperatures outside are exceedingly low. Consequently, this helps save on energy costs.

2. Minimizing Moisture-related Issues

During the winter, the hot water PEX pipes can sweat due to temperature variations, leading to condensation. Insulating the pipes can prevent condensation and other moisture-related problems like mold growth.

3. Prolongs PEX Lifespan

Insulation protects PEX from exceedingly cold temperatures that could cause the pipes to split or crack over time. As a result, this ensures the piping lasts longer, up to 50 years or more.

4. Prevents Costly Repairs

When PEX is exposed to freezing temperatures for extended periods, the pipes can develop leaks along the joints. If the leaks are not detected and repaired early on, the walls could also get damaged, requiring expensive repairs. Insulating the pipes helps you save money on repairs.

What to Consider When Insulating PEX?

Before insulating PEX, you must consider several things to ensure the best results. These include:

1. Type of Insulation Material

There exist several types of insulation materials for insulating PEX pipes. The most common ones are foam pipe, radiant barrier, and fiberglass insulation.

Polyethylene foam pipe insulation is a tube-shaped foam that is economical and easy to install. However, the foam is a severe fire risk and requires a thermal barrier for enhanced safety.

Radiant barrier insulation is a reflective material that reduces heat transfer by reflecting thermal radiation instead of absorbing it. However, unlike foam, a radiant barrier is not very effective in colder climates. It works best for warmer climates.

Fiberglass is also low-cost and easy to install insulation. On the flip side, it is quite rigid and more vulnerable to moisture than other insulation materials.

2. PEX Pipe Insulation Requirements

The standard insulation for PEX is copper tubing size (CTS), according to the American Standards Institute. This means you can insulate PEX with the same insulation sized for copper pipes.

3. PEX Sizing

PEX piping comes in standard sizes that range from 1/4 to 3 inches per CTS (copper tube size). However, their length varies. So, you will need a tape measure to determine the size of all the PEX in your house that need insulation.

This will help you know exactly how much insulation material you need for the whole project.

4. Insulation Thickness

Generally, the thicker the insulation material, the better it works to minimize heat transfer. PEX pipes exposed outdoors require a minimum of 3/8-inch thick insulation material. But if you live in areas with colder climates, you should use at least 5/8-inch-thick insulation material or more.

5. R-Value of the Insulation

R-Value is a measure of how well the insulation material can resist the heat that travels via it. So, the higher the value, the better the insulation in terms of thermal resistance.

Typically, foam pipe insulation boasts a 2-per-inch R-value. However, a heavy-duty foam pipe’s R-value is 4 per inch. On the other hand, the thermal resistance of closed-cell spray foam is 6.5 per inch.

Likewise, the value of fiberglass ranges between 2.2 and 3.8 per inch, depending on its density and formulation. However, the radiant barrier lacks thermal resistance since it reflects instead of absorbing heat like other insulation products.

What Is The Best Insulation for PEX Pipe?

Closed-cell foam insulation is the best and most commonly used for PEX piping. This is because it is eco-friendly and has the highest R-Value at 6.5 to 7 per inch. Therefore, its thermal resistance is better than that of other insulation materials like fiberglass and heavy-duty foam pipe.

On top of that, closed-cell foam is much thicker and expands to approximately 1 inch thick when installed. This feature comes in handy because PEX is also known to expand. Even better, the foam acts as a water and moisture barrier, helping deter mold.

How To Insulate PEX?

Most insulation materials available, including foam and fiberglass are easy to install. So, below are step-by-step instructions on how to insulate PEX.

  • Step 1: Use a clean rag to wipe any dirt, moisture, or dust on the surface of the PEX.
  • Step 2: Choose the type of material to use. You can choose between foam, radiant barrier, and fiberglass.
  • Step 3: Determine the length of the PEX pipes you want to insulate using a tape measure.
  • Step 4: Use a utility knife to cut the insulation material based on the length of your PEX tubing. You can add a few extra inches of insulation material at each end for a secure fit.
  • Step 5: Slide the PEX insulation sleeve onto the pipes or wrap it around, ensuring it covers the entire tubing’s length.
  • Step 6: Use adhesive or tape to secure the foam in place based on the manufacturer’s instructions.


In this section, we will respond to frequently asked questions regarding how to insulate the PEX pipe underground.

Is it worth insulating hot water PEX pipes?

Yes, because PEX has no significant insulating properties of its own. Therefore, insulating the pipes will ensure the hot water stays warmer longer, especially during the colder climates, preventing freezing.

Can I insulate PEX myself, or should I hire a professional?

If you have basic handyman skills, you can do the installation yourself since most insulation materials are easy to install. However, if you are uncomfortable or unsure about the task, you can hire a professional plumber to avoid improper installation.

How do I insulate the PEX pipe in the crawl space?

The best way is to use foam and run it along the entire length of the PEX pipes. Then, close the crawl space vents during the winter for maximum insulation. You could also winterize your house or run the faucets to keep the pipes in good shape.

Final Thoughts

PEX does not need to be insulated if it passes via insulated interior or exterior walls. However, if you live in regions with harsh winters and the PEX pipes are exposed or installed in uninsulated areas, you must insulate them. This will help protect the pipes from freezing and bursting, preventing costly repairs.

Insulating PEX yourself is easy. However, before anything else, you must consider the insulation type to use, insulation requirements, PEX sizing, and insulation thickness. With that said, the best insulation for PEX pipe is closed-cell foam, thanks to its high R-Value.