5 Common Myths About RV Insulation

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This article about RV insulation was written for rvinspiration.com by RV manufacturing expert Ross “The RV Engineer”. RV engineer by day, blogger by night, and grumpy coffee-drinker by morning, Ross “The RV Engineer” helps RV owners demystify the inner workings of modern RVs and campers. For analysis and answers of camper tech talk and RV tips, check out his website, AskTheRVEngineer.com.

There’s this vein above my temple that throbs every time Joe the RV Salesman rehearses one of these five myths about RV insulation. These falsehoods just won’t die, and unfortunately, even some RV manufacturers seem to believe them!

Understanding RV Insulation: What Is R-Value?

R-value is just a number indicating how quickly a material will transfer heat. High R-value = heat insulator. Low R-value = heat conductor.

• A 1-inch thick wood board has an R-value of about 1.
• A 1-inch thick strip of fiberglass batting has an R-value of about 3.2
• A 1-inch thick block of Styrofoam has an R-value of about 5.

The thicker the material, the higher the R-value.

Also, it’s helpful to know that heat can be transferred in three ways: conduction, convection, and radiation. As you’ll see, a lot of myths confuse these three!

Myth 1: R-Value Matters for RV Skirting

Skirting is an interlocking wall of panels around the base of your RV. They are commonly used when cold-weather camping with conventional travel trailers and fifth wheels.

Here’s what the myth says: “The skirting panels must be insulated and have a high R-value.”

But the truth is that it’s not about R-value; it’s all about airflow!

Skirting your RV stops cold air from flowing underneath your trailer floor, sucking away heat, and blowing it away. In other words, skirting allows the air itself to do the work! Leaking warm air heats the air, and the skirting traps it in place.

To read about the pros and cons of all the different types of RV skirting, check out this article.

Myth 2: Sales Brochures Convey the Actual R-Value 

When it comes to R-value, what you see isn’t what you get! 

For instance, many RV manufacturers will say, “Our wall is R-11.” Usually, this means one of two things:

1. The walls have a 2-inch foam core with internal aluminum tubing, or
2. The walls have 16-inch wide fiberglass batt insulation stuffed into stud bays made from 2×2 (1-½ x 1-½ actual) wood framing.

In the first case, the manufacturer has not accounted for the waste bridging heat from the aluminum tubing. And that can reduce the whole-wall R-value by 10-30%!

In the second case, fiberglass batting has an R-value of about 2.2 – 3.5 per inch. Period. Stuffing batting designed for a 2×4 wall into a 1.5-inch thick wall does not an R-11 wall make! The walls would need to allow the insulation to expand to the size of the space it's designed for in order to achieve its potential R-value.

Myth 3: Fiberglass RV Insulation Is a “Tried ‘n’ True” Solution

Many entry-level “stick ‘n’ tin” RVs still use fiberglass batting for insulation in their walls and ceilings. While installation methods have improved, fiberglass remains one of the worst choices for RV insulation.

The jarring, bumps and vibrations of a traveling RV can cause the fiberglass to settle and compress, leaving empty cold spots. Most manufacturers try to alleviate settling by gluing the batt facing to the plywood sheathing, but foam insulation is a better choice, and a layer of foam insulation inside the walls is something you'll want to look for when shopping for a four-season RV.

Most importantly, fiberglass should never get wet! When wet, it loses its R-value, and it will quickly grow mold. An undiscovered roof leak or significant interior condensation can quickly ruin an entire sidewall!

Myth 4: Reflectix Window Covers Are Great for Cold Weather Camping

There’s actually a grain of truth in this myth. Yes, DIY reflective covers are great…for hot weather. Thanks to the aluminum foil, they do a wonderful job at reducing solar heat gain by reflecting the sun's rays away from the RV.

But Reflectix is radiant heat insulation, meaning it reflects heat. In order for the foil to work, the reflective side needs to be aimed at an empty space that it can bounce heat through.

In dark or cold weather, you wouldn't want to reflect heat away from your RV, and rather than trying to hold in heat by reflecting it back into your RV, it would be more efficient to allow the sun to pass through the glass and warm your camper via the greenhouse effect, so the only value they provide as insulation comes from the bubble wrap backing, which adds an extra layer of conductive insulation…but there are far better options for insulating RV windows that won't block the sunlight from warming the interior of your RV.

Myth 5: R-30 Insulation Is Actually a Thing

Any time you see a sidewall R-value above R-10 or a roof R-value above R-15, beware.

I’m not saying it’s impossible. But it’s rare. There is no enforced testing standard, so RV manufacturers can (almost) claim any R-value they want!

Most of the time, claims of R-30 or R-40 indicate that the manufacturer is using reflective foil-faced bubble wrap, a.k.a. Reflectix. Now, I don’t have time to dissect the full scope, but take my word for it: 90% of the time, the insulation has been improperly installed and is hardly worth anything!

Remember, even excellent insulators like foam board still only achieve about R-5 per inch. If a roof is 3-1/2 inches thick and the manufacturer is claiming R-30, you call BS on that.

Head spinning? Not sure who you can trust?

Well, I’ve got good news for you! You can trust Ashley Mann, head honcho here at rvinspiration.com. Head over to her winter RVing resource page for DIY ideas for improving your RV's cold weather readiness. And if you’ve got other questions about the technical components of RV's burning in your brain, here are some more RV FAQs answered at AskTheRVEngineer.com!