Let’s Talk About Vapor Barriers and Thermal Bridging
A quick guide to understanding where a vapor barrier goes in your van or bus build, and why it matters. This post also highlights how to reduce moisture buildup and prevent thermal bridging for a better-insulated, longer-lasting rig.
(Yes, You Should Care)
Before you decide this topic sounds too technical or confusing, hang tight—I promise it’s not as complicated as it seems. Here’s the quick and simple difference: vapor barriers deal with moisture, and thermal bridging is all about heat. Once you know that, everything else starts to make a lot more sense.
What the Heck Is a Vapor Barrier (and Why Should You Care)?
If you’re working on your rig and trying to figure out how to keep it warm, dry, and mold-free, vapor barriers are something you really want to pay attention to—even if it’s not the most exciting part of your build.
A vapor barrier is a layer of material that helps stop moisture in the air (aka water vapor) from sneaking into your walls, ceiling, or floor—places where it can cool down, turn into condensation, and cause mold, mildew, or even damage your insulation. Not exactly the kind of surprise you want when you’re living simply on the road.
Why It Matters in a Rig
Rigs go through some serious temperature and humidity swings. Whether you’re parked in a winter wonderland or melting in the summer sun, condensation can become a real issue. And once that moisture gets inside your walls? It’s not easy to dry out—and it definitely isn’t cheap to fix.
That’s why vapor barriers are usually placed on the warm side of your insulation. In colder climates, that means the interior side of your wall. In hot and humid areas, it may go on the exterior side. The goal is always the same: stop warm, moist air from reaching a cool surface and turning into water.
What Can You Use as a Vapor Barrier?
Here are a few options you might consider (and possibly link later):
- Foil-faced insulation (like polyiso with a foil backing)
- Reflectix or other aluminum bubble wraps
- Plastic sheeting
- Specialty vapor barrier coatings or paints
- My favorite and easiest is Vapor Barrier Tape
Reflective insulation, like foil or aluminized polyester, works by reflecting heat and slowing down how moisture travels. When a product does both—blocks heat and moisture—that’s a huge win in a small space.
This part of the build might not get a lot of glory, but it’s one of those quiet victories that keeps your rig cozy and healthy over time. I totally get the temptation to skip it (I’ve been there too), but future-you will thank past-you for doing it right.
Now for the Other Not-So-Sexy Topic: Thermal Bridging
If you’re building out your rig, you’ve probably heard the term thermal bridging tossed around. Sounds super technical, right? But it’s really just another way heat (or cold) can mess with your comfort—and it’s surprisingly common in rigs.
Here’s the deal: thermal bridging happens when heat or cold finds an easy path through a material like metal, bypassing your insulation entirely. Think of it like a shortcut through your wall—only instead of saving time, it robs you of warmth (or coolness) when you need it most.
So, What Causes It?
Thermal bridging shows up in all kinds of sneaky ways:
- Metal studs, screws, bolts, and window frames can act like little highways for heat or cold.
- Insulation gaps—even small ones—leave weak spots where outside temps sneak through.
- Poorly sealed joints (where walls meet the roof or floor) create easy paths for heat transfer.
I know it sounds like a small detail when you’re in the thick of a build, but it really is a “handle it now or pay for it later” kind of thing. Cold spots, weird drafts, and uneven temps are annoying, sure—but the real issue is condensation.
Why It Matters for Nomads
Here’s the big red flag: when a part of your wall gets cold enough—thanks to thermal bridging—moisture in the air can turn into little water droplets on the inside of your rig. That leads to mold, mildew, and musty smells that are hard to ignore in a small space.
Worse still, if thermal bridging gets bad enough, you might have to tear open your walls to fix it. Nobody wants to rip out their living space to repair something that could’ve been prevented during the build. So yeah, it’s worth thinking about upfront.
How to Prevent or Fix Thermal Bridging
Wrap Everything in Insulation
A continuous layer of insulation helps stop heat from finding gaps or weak spots in your walls. This is why spray foam is so popular—it fills in cracks and hugs every surface. That said, spray foam isn’t always practical, especially in smaller vehicles or if you’re doing the work yourself.
Use Heat-Blocking Materials
Anywhere heat might want to sneak in—like metal framing or around windows—use materials that slow it down. Reflectix is a great option for doors and windows. In fact, a quick tip: placing Reflectix on the outside of your rig during hot days helps keep that heat from ever making it through the glass in the first place.
Install Insulation Like You Mean It
Even tiny gaps in your insulation can cause big issues. Cut your insulation to fit snugly, and don’t rush this part. Gaps around corners, wires, or curves might seem small now, but they’ll mess with your comfort later.
Pick Materials That Work for You
Some materials naturally help reduce thermal bridging. Rigid foam board works well in walls, cotton batt insulation is great for ceilings, and thermal curtains can make a big difference around windows. You don’t always need the fanciest product—just the right one for your build.
Seal the Trouble Spots
If you’re upgrading an older rig, go back and seal the obvious problem areas—like corners, seams, and metal contact points. Even a few hours of attention here can improve your interior temps a lot.
How This Plays Out in Different Rigs
When it comes to insulation and thermal bridging, the type of rig you have matters. Here’s a quick comparison:
Cars
Surprisingly, cars are often better insulated than you’d think. They’re designed for passenger comfort, so they’ve got insulation built into doors, dashboards, and floors to reduce noise and regulate temperature. That makes them pretty efficient for such a small space.
Buses
Buses tend to have some insulation, especially in the ceilings and floors, but their main goal is durability and space, not comfort. You’ll need to add more insulation yourself if you want to keep things comfy.
Vans
Vans are hit or miss. Cargo vans usually don’t come with much insulation, but camper vans or those designed for travel might be better equipped. Still, if you’re starting with a bare shell, you’ll want to handle insulation from the ground up.
Bottom line? Cars win in terms of factory-installed insulation, but buses and vans give you more room and control to do it your way.
Getting Real: My Own Rig Situation
To really prevent thermal bridging, you need to strip the rig down, insulate it thoroughly, and seal every seam. I haven’t done that in my current van—partly because the interior is still in decent shape, and partly because, let’s be honest, I’ve been in a bit of a lazy phase.
And you know what? I can definitely feel the difference. When it’s cold outside, I feel it. When it’s hot, same deal. So while I know what I should do, I’m being real with you—sometimes you just don’t have the energy or budget to rip everything apart. And that’s okay too.
When it comes to cars, I honestly think it’s harder to insulate them properly, and depending on how you use the space, it might not be worth the effort. You can manage temps pretty well in a small area with the right layers, fans, and window covers.
Might not be a popular opinion—but I’m sharing it anyway.
In Essence: A Quick Recap (No Quiz Required)
Still wrapping your head around all this? Let’s boil it down one more time:
- Vapor barriers = moisture protection. They stop condensation from forming inside your walls and messing with your insulation.
- Thermal bridging = temperature problems. It’s when heat or cold travels through conductive materials, bypassing your insulation and causing cold spots, drafts, or worse—mold.
Neither topic is exactly thrilling, but trust me—they matter when you’re living tiny and trying to stay comfortable. Taking the time to insulate well, seal your rig tight, and prevent heat or moisture from sneaking in can make a huge difference in how happy and healthy you feel in your space.
You don’t have to be perfect. But a little effort now can save a whole lot of hassle later.
