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 to 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!

We are going to dispel these myths right now so you can outsmart the RV salesman and understand your RV insulation.

Are RVs insulated?

This is a great question to start. Yes, all RVs are insulated to some degree, though not all are insulated for winter.

Every manufacturer will use different materials for insulation. Common types of RV insulation include wood, fiberglass batt, spray foam insulation, and rigid foam board. Foam board insulation is the best option with a high R-value and is most common on newer RVs.

Every RV will have a different R-value for its insulation depending on what materials are used.

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. Lower 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.

Key takeaway: No matter the material thickness, skirting is crucial insulation against cold weather.

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 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.

Key learning: The compressed thickness of insulation determines the 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. Foam insulation is a better choice, and a layer of spray 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!

Key learning: If you’re building out a camper and trying to choose your insulation, foam insulation is the best way to insulate an RV trailer.

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. 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. This 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.

Key takeaway: Something clear like bubble wrap would be better than Reflectix for insulating RV windows.

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, RVers call BS on that.

Key Takeaway: Ask how many inches thick the roof is and calculate the R-value on your own instead of trusting Joe the RV Salesman.

How do I insulate my RV for winter?

There are a few key ways to insulate your RV for winter—and surprisingly none of them involve your typical insulation. Follow our cold weather checklist to prep your vents, pipes, and tanks before winter.

Learn How: How to Prepare Your RV for Cold Weather

Does insulation affect winterization?

No matter how well insulated, you should always winterize an RV before you store it in cold temperatures.

Before storing your RV, be sure to follow this 23-point checklist.

Before winter, don’t forget to fully winterize your pipes to avoid costly damages. For the step-by-step process, follow our winterization guide here.

How do I insulate my RV underbelly?

The underbelly of your RV is where your pipes and tanks are likely exposed. (Unless you have a four-season RV with an enclosed underbelly.)

To insulate your RV underbelly, we recommend installing RV skirting. Lightweight foam board can be the least expensive and best option.

Learn How: How to Make Foam Board RV Skirting for $100 This Winter

Ask the Experts

If you’ve got other questions about the technical components of RVs burning in your brain, here are some more RV FAQs answered at AskTheRVEngineer.com!