DIY Van Insulation Explained

Insulating the van is essential as it decides how comfortably someone will live in it. Insulation can achieve in many ways using various materials. People are sharing mixed comments all over the internet based on their experiences, which is why this is one of the most debated subjects in the van dwellers community. 

I’m sharing some facts and options to help you with your final decision.

How important is van insulation?

Sprinter, Promaster, or any cargo van is not purposefully built for a full-time living when released from the factory. It is a metal tin. So what happens when you keep a metal tin outside directly exposing it to the sun or cold weather? The inside gets either hot or cool depending on the ambient condition. So the van may need to use a larger A/C or heater to make it livable. I doubt whether the desired result can achieve with poor insulation.

If you are new to this domain, you might hear a couple of terms down the line when you expand your research. So let me quickly give a quick summary of how heat transfer works.

Heat transfers when there is a temperature difference. Normally heat transfers from warm to cold temperature. Insulation is trying to break or minimize this transfer. The ultimate goal is to maintain a comfortable temperature inside the van regardless of the outside temperature. A cold atmosphere if the outside is hot and a warm atmosphere if the outside is cold.

There are three different ways to transfer heat. Those are Conduction, Convection, and Radiation


Heat transfers through the material when there is a temperature difference. Some of the material thermal conductivity in watts per meter-kelvin is as follows. Materials with higher values do better conduction.

MaterialThermal conductivity (W/m K)
Water at 68 ℉0.6
This table shows the thermal conductivity value of copper, steel, water, glass, iron, and aluminum.

Sprinter van body made of a combination of steel and aluminum.


Convection is the transfer of heat with movement. The medium can be either fluid or gas. Hot air goes up, and cold air goes down. Air move in a circular motion and transfer heat through hollow spaces in the van.


Heat transfer through electromagnetic waves. Radiation is the reason you feel the heat from a bonfire when you are close to it.

A suitable insulation method needs to cover all these three aspects to provide better insulation.

That’s mainly about the heat transfer. The next problem with the insulation is condensation and moisture control.

Your body evaporates moisture and moisture coming from cooking, drying out wet clothes. The fresh air that comes from the outside can contain moisture. So this moisture air tends to condensate and form water droplets on smooth surfaces when there is cold air outside. If this water evaporates soon, then there is not that much problem. But if this water collects and moisture starts to build up in dark corners over time, this can eventually lead to rust and mold issues in the van.

Below terms are often used when comparing different insulation materials.  


Insulation materials can be natural, synthetic, or hybrid with different sizes. So there should be a way to compare materials to each other regardless of their nature. Effectiveness of the insulation measure using R-value. It denotes how effectively the underlying material is resistant to the heat flows. The higher the R-value, the greater the insulating power.

The R-value depends on the type of insulation, its thickness, and its density. Typically this value is noted as per inch thickness, like 3.6 per inch. So if you apply this material two inches, then R-value increases to 7.2. 

Thermal bridge

A thermal bridge flows heat across the insulation through a non-insulated path. Let’s say you filled up all walls/cavities in the van but left pillars/ribs without insulating it. Those are creating thermal bridges. These small leaks will significantly affect the overall insulation performance in your van.

Thermal break

The way to prevent thermal bridges call thermal breaks. 

Vapor barrier

Previously I explained the condensation issue and the vapor barrier used to prevent that. Typically a vapor barrier installs over the insulation. 


Some materials release harmful fumes during installation and after. So it’s crucial to identify whether the insulation is off-gas for a longer time. For example, spray foam is off-gas heavily within the first 24 hours of applying. It is continually off-gas the rest of the years, but it says that amount is negligible if it properly cures. 

Thermal drift

Decreasing the R-Value over time in the insulation is called thermal drift. Foam-based insulation materials contain tiny cells that trap blowing agents(chemical gas used during manufacturing). Over time, these blowing agent gas escapes from the material and compromises the R-Value by displacing it with ordinary air. 

Does the van color matter to the insulation?

Yes, it does. When the sunlight hits the van body, a portion of the light gets converted to heat, and the rest reflects. This heat absorption may depend on the color and other factors. All energy that is not reflected or dissipated to the atmosphere transmit to the interior as heat energy. So the color of the paint plays a significant role here.

Lighter color has more reflectance than a darker color. White color has SR = 71.61, SRI = 87 and black color has SR = 25.00, SRI = 23

SR: The fraction of solar energy that reflects by the roof surface (Scale 0 to 100)

SRI: A calculated value that combines solar reflectance and thermal emittance into one number

Van Insulation materials

Thinsulate SM600L

Thinsulate is one of the popular choices among van builders. This lightweight material comprises polyester and polypropylene fibers with a single black scrim. It doesn’t off-gas any chemical fumes or loses any fibers into the air. 

The factory packaging comes as a compressed sheet and will expand up to 1 ¾ inch once you use it. This material is Hydrophobic fiber which means it doesn’t retain any moisture. So it resists mold and mildew. Thinsulate weight is 0.13 lb per square foot. So approximately 39.5 lb of weight will add to the Sprinter 144 van.

R-Value: 3.3 per inch

You may need approximately this much Thinsulate to insulate the walls, ceiling, doors, and cab if you purchase 60-inch width rolls. 

144″60 linear feet
170″70 linear feet
170″ Extended80 linear feet
130″50 linear feet
148″60 linear feet
148″ Extended70 linear feet
136″50 linear feet
159″60 linear feet
159″ Extended70 linear feet
Amount of Thinsulate that requires to each van model

Sheep’s Wool


People have been using sheep wool as thermal insulation for centuries. In addition to that, wool has good sound attenuation properties as well. It is 100% natural material which means it is biodegradable and does not pose any environmental threat.

Wool doesn’t produce any fumes like other chemical synthetic products. It absorbs moisture and releases it back to the air when the ambient condition changes. So you may not face any condensation problem with wool. Usually, wool is treated with a non-toxic solvent to prevent insects’ attraction.

R-Value: 3.4 per inch

2-inch thick wool batts weigh approximately 0.18 lb per square foot. So about 56.5 lb of weight will add to the Sprinter 144 van.

Van TypeCoverageNumber of Bags
(100 square feet each)
Sprinter 144300 square feet3
Sprinter 170375 square feet4 – 5
Sprinter 170 Extended400 square feet4 – 6
Transit 148325 square feet3 – 4
Promaster 159325 square feet4
Mercedes Metris225 square feet2 – 3
Chevy Express225 square feet3
Nissan NV325 square feet4
Amount of Sheep’s wool requires for each van model.

Compressible insulation materials like Thinsulate, wool, etc., should not be compressed after installation. The application gives the best results when materials are in fully expanded mode. It reduces the R-value by compressing. So remember this and pick appropriate material for the location.

Rigid Foam Boards


Rigid foams are a kind of plastic material manufactured with numerous tiny cells. These cells are fully enclosed and often filled with certain types of gas called blowing agents. Some of these gases have an environmental impact.


Expanded Polystyrene is closed-cell beads. These are expanded and fused using steam and blowing agents. The final insulation has significant open space between the beads and traps 98% of the air. EPS provides the highest R-Value per dollar value in the rigid foam category.

Don’t use any environmentally impact blowing agents during the manufacturing process. No thermal drift over time and doesn’t off-gas. But water can penetrate and trap in open spaces and build up moisture.

R-value: 3.85

XPS Rigid Board

Extruded Polystyrene is another closed-cell board. XPS is a tightly compact material compared to the EPS due to the extruded manufacturing process. It does thermal drift over time but provides better R-Value at a lower temperature. The maximum service temperature is typically limited to around 165 ℉. 

XPS is a little bit pricier than the EPS. Provide better R-Value and water absorption resistance over EPS. XPS will off-gas a little bit in the long run.

R-Value: Initially 5.0 at 75 ℉, 6.0 at 15 ℉, and with the aging, this reduces to 4.7

Polyiso Rigid Board

Polyisocyanurate or Polyiso is a closed-cell foam laminated panel. This compound is also available as a liquid and sprayed foam as well. Polyiso provides a better service temperature range from -150 ℉ to 250 ℉, but the R-Value decreases with the temperature drop. The blowing agent gas used in Polyiso condenses at a lower temperature and increases the thermal conductivity.

Polyiso does thermal drift over time, but laminated panels delay this effect significantly.

R-Value: 6 at 75 ℉, 2 at 15 ℉

Spray foam


Spray foam insulation comes in both open and closed-cell materials. But make sure to pick the closed-cell option to prevent moisture build-up. This insulation is somewhat a permanent solution, and it is a tedious task to remove once you apply it.

This spraying can be done either by yourself using a DIY spray kit or with the help of a professional spraying company.

Spray foam insulation heavily off-gasses within the first 24 hours during the curing process. It says roughly 98% of toxic gas will release within that period. The rest will be off-gas over time, and it says the exposure amount is negligible to pose any threat.

The best advantage of using spray foam is covering all nooks and crannies. But applying too much foam can cause the sheet metal to warp.

R-Value: 6.5

Mineral wools

Mineral wools are one of the most popular materials in residential construction. Rock wool(stone wool) and glass wool (fiberglass) fall under this. These usually come as semi-rigid batts. Both rock wool and fiberglass are vapor permeable, which means water vapor travels through the material. 

Rock wool

Rock wool’s main ingredients are basalt rock(volcanic rock) and slag(a by-product of steel production). Based on their proposition of basalt and slag, it calls rock wool or slag wool.

Rock wools are inorganic and resistant to mold, fungi, and bacteria. Rock wool insulation is hydrophobic, which means it does not absorb water or hold moisture. But condensation build-up in between the rock wool insulation and the sheet metal due to the vapor-permeable property allows it to dry out.

There is no thermal drift with rock wool.

R-Value: 3 – 4.2


Fiberglass retains water and moisture. So fiberglass is not a good choice for van insulation. 

R-Value: 2.2 – 3.8

Recycled Denim Batts

Denim batts retain water and moisture, so they are not suitable for van insulation.

R-Value: 3.5

How much will AC cost?

It is challenging to achieve a comfortable temperature inside the van, even with the insulation. Insulation delays the van from getting into the surrounding ambient temperature. Internal temperature can reach as high as 170 ℉ when left under the hot sun in summer without proper ventilation.

So you may need either a heater or an Air condition unit based on the outside temperature. A proper van-compatible air condition unit can range between $700 – $3000.

An air conditioner can reduce internal van temperature into a comfortable range. Depending on the fan speed, the typical 5000 BTU air conditioner uses 29-38 amps @ 12.8 Volts, and the 8000 BTU uses 42-49 amps @ 12.8 volts.

On a median fan speed, 5000 BTU units would require 160 amp-hours to run 5 hours. 8000 BTU would need about 235 amp-hours. 

So depending on how hot the temperature is and how good your insulation is, it would be a good idea to keep at least 200-400 more amp hours only dedicated to an AC unit.

Most dwellers avoid adding an AC unit due to the high cost of the unit and the requirement of an additional battery bank.

Why does van ventilation play a significant role?

Cooking, sweating, breathing, etc., will generate lots of moisture inside the van. This moisture condensates in stagnant spots and builds up water vapors/droplets. There should be a way to remove this excess moisture out of the van to prevent this. 

The internal temperature will slowly rise on a hot day, even with insulation. A suitable vent fan can help with controlling both moisture and temperature. 

Cross ventilation is the easiest way to tackle soaring heat on a hot sunny day. An airflow helps carry out heated air with moisture out of the van.

A single fan with an open window will create cross ventilate airflow. Two vent fans give better circular air movement that one pulls air out, and one pulls in. Especially LWB models like Sprinter 170, 170 Ext should have two fans set up for the ideal living condition if there is no AC unit.

Why is window covers a must for the van?

All the hard work on insulation goes in vain if you do not cover your windows. Heat will penetrate during warmer days, and heat will lose on cooler days through windows. You can easily make window covers using fabric and materials like Reflectix EZ-Cool. Just use small magnets to stick. The windshield is the biggest culprit, and address that adequately. 

There would be like 15 degrees temperature difference between the cabin and the living space on a sunny day. So adding a thick curtain to separate the cabin and the living space is also a good option.

Window films like ceramic or 3M crystalline window tint can reduce massive heat penetration by around 35% or more while within the legal limit.

Does the van need a vapor barrier?

The intention of adding a vapor barrier is to seal off the internal metal surface and the insulation from exposure to any moisture. But it is tough to achieve this with 100% success. Not only does the vapor barrier itself fail due to slits and joints, but there are many places where moisture penetrates from the van structure. 

So eventually, the moisture will trap between the metal sheet and the vapor barrier and causes rust, moisture problems like mold that defeat the purpose of its original intention. 

So it’s a waste of money to add a vapor barrier, and that money should invest in proper ventilation.

How important is sound deadening/dampening for a van?

Some insulation materials have sound-deadening properties. But whether insulation provides the sound deadening or not, it is highly recommended to use a dedicated sound deadener like KILMAT, FatMat Rattletrap, or Noico.

Usually, road noise is too high, and insulation alone can’t provide a comfortable level of sound deadening. You don’t need to apply sound deadeners all over places in walls, ceiling, and the floor.

Sound deadener material doesn’t need to cover the entire van 100%. Covering 25% of each panel space starts to give a good result if the selected insulation material has some sound deadening properties.

Anyway, covering beyond 65% of the area would be a waste of money. Wheel wells need to be fully covered with sound deadeners since wheels are significant noise contributors when the van moves.

Insulation options

Compressible insulation materials like Sheep’s wool, Rockwool, and Thinsulate lose R-Value if they get compressed. There should not be any air pocket between the metal sheet and the rigid foam insulation to avoid moisture build-up.

Polyiso loses R-Value when the temperature drops to subzero temperature. XPS’s maximum service temperature is 165 ℉. 

So it is a bit difficult to get proper insulation only using a single insulation material throughout the van. 

The better option is to go for several insulation materials considering the durability, material thickness that needs to apply for better insulation, and R-Value per dollar value.

So our choice of insulations is as follows.

  • Sheep’s wool or Thinsulate
  • Polyiso or XPS
  • Rockwool
  • Spray foam

Try to stick with Sheep’s wool, Thinsulate, Polyiso, and XPS if possible. These insulations are easy to install and give minor health concerns.

If you are fully environmental and health-conscious, Sheep’s wool will be the best option for the entire van. Wool is the ideal insulation for the wall since some wall cavities have enough depth to get a better R-Value. But sometimes, typical 2-inch wool insulation might not be enough for the ceiling on some scorching sunny days. But proper ventilation will help to reduce the discomfort.

Van comes with weep holes to drain any liquid. These holes can drain excess water that builds up due to condensation. So make sure not to cover those holes while insulating.

Use any hydrophobic material like pieces of tubular (slit foam) pipe/copper tubing insulation at the bottom to keep insulation from settling/sagging as the vehicle ramble down the highway. 

Floor insulation gets poor attention most of the time. Some think the factory-fitted OEM floor is enough to block the radiant heat. But it needs insulation if the ambient temperature gets much colder. 

It is better to use a frame to fit insulation, whether compressible or rigid, ideally with 1 inch or 1 ½ inch height. Compressible materials will not give the best performance without a frame to secure them. 


Rigid boards like Polyiso or XPS will degrade the insulation properties if cut into smaller pieces. It will speed up the off-gassing by cutting it into smaller chunks. So don’t assemble a frame with a smaller area and stuff rigid boards into it.

XPS, Minicell, Thinsulate SM200L, or Thinsulate AU4002-5 fill the floor corrugations. But filling the corrugation is optional. Either put the frame or rigid foam insulation like XPS, Polyiso 1/2 inch – 1 ½ inch layer.

Another option is covering with Minicell. Use OEM factory floor cover if it’s in good condition or lay ½ ich plywood layer, preferably Baltic Birch top of this insulation frame. Finally, finish with a vinyl floor. 

Securing these layers with the metal base floor is optional. It will stay on the floor because of the weight of the cabinets, bed, etc. But use proper adhesive to secure rigid foams to prevent squeaks. Better to secure edges using spray foam to eliminate unwanted noises when driving or walking. Canned spray foam like Great Stuff can use for this purpose.