The Best Types of Shipping Container Insulation


Insulation is the material that divides you and your comfortable room of conditioned air from the extreme temperatures outside. When thinking about insulating a shipping container, there are quite a few possibilities, each with its pros and cons.

You likely require insulation for your shipping container home, but which type of insulation is best? The answer can alter depending on your circumstances and goals.


In this Article

This article will solve all your problems regarding shipping container insulation. Storage container homes are trendy these days, but you need to know what it takes to turn them into a living area truly.

We will first examine the most relevant considerations in choosing a type of insulation. We will examine the insulation types you can pick from, and we will conclude with some insulation options.

You may have heard that polyurethane spray foam insulation is the only variety worth considering for shipping containers. As you'll find out below, that's not always the case.

Our goal with this article is to give you a comprehensive guide to understanding insulation generally and how to choose the type of insulation that is most suitable to your needs. This can incorporate factors such as the container's size, geography, climate, and insulation-specific attributes like price, quality, and more.

With that stated, let's start with a discussion of controlling factors and the various sorts of home insulation.


What is Insulation?

If you had an open-air porch or patio hot in the summer, would you air-condition it? Not without enclosing it by building walls first, of course! 

You need to keep the conditioned air (air that has been intentionally cooled or warmed, depending on the season) separate from the outside air. Otherwise, you're air conditioning the community.

If you built the walls around your porch out of newspaper or plastic food wrap, they wouldn't be very effective at regulating the temperate (even though they would keep the air separated). 


Why not?

A thin wall container prevents heat transfer from the warm side to the cool side very effectively. While the actual air can't move through the wall, the air in the air CAN move through the wall material. So even though the air is separated, your energy efficiency would be quite low. We'd recommend checking out our article on heat transfer in container homes before you go any further if you're not clear on any of the concepts so far!


Therefore, insulation is a material specifically designed to prevent heat energy from moving through the walls (and ceiling, and floor) of your shipping container home. It generally works by trapping air or other gasses in a complex matrix of tiny cells or passages. 


Compared to solids and liquids, gases conduct thermal energy poorly, making them excellent insulators. By confining the gases to millions of tiny cells, you reduce the role convection plays within the gas, further increasing the material's insulating properties.


In most cases, when we talk about thermal insulation, we're specifically talking about conductive (and, to a lesser extent, convective) heat flow. The resistance to this heat flow is measured using an "R-value," which coincidentally is how insulation is rated (higher is better). Heat flow via radiation does come into play, as well as discussed below.




Why do you need container home insulation?

When insulating a shipping container, you're separating the conditioned airspace from the outdoors. It's the same thing you'd do with almost all enclosed structures that have climate control. As explained before, insulating material helps keep the heat from the warmer side moving to the cooler side. This improves your container home's energy efficiency by reducing the energy required to regulate the inner temperature.

Unlike some more traditional residential construction types, shipping container homes have the added issue of an exterior that is entirely made of steel. Given how great steel is at transferring thermal energy, it is especially ineffective at keeping your airspace at a different temperature than the air outside. Therefore, insulation is often required more for shipping container homes than for other architecture types.

And let's not ignore that the steel of container home can absorb a tremendous amount of radiant energy from the summer sun, actually getting hotter than the ambient air. Stated, unmodified shipping containers are exceptional at blocking outside air from getting inside. However, they perform inadequately at keeping heat from passing through their walls.

Nevertheless, just because container homes are poor at preventing heat transfer doesn't automatically mean you need insulation. The other determinant to consider is the climate.




How climate affects your insulation decision

Suppose you are fortunate enough to live in a location with a suitable climate for you to live in without additional cooling or heating. In that situation, you may not need insulation material for your shipping container—areas like southern California and parts of the Mediterranean feature what many consider to be an ideal climate. 


With that said, some people still need heating, and air conditioning in these climates…and thus should strongly consider insulation. Whether you will need climate control for your shipping container home or not depends on your personal preferences for what is 'comfortable.' With additions of fans in warm climates and warm clothes in colder ones, you may be able to manage the normal temperatures without any added insulating material.


If you don't live in such a location, we strongly recommend you insulate your storage containers, but you don't HAVE to. You'd need to weigh the costs of insulating (a one-time cost) versus the ongoing heating and cooling expenses to run your air conditioner and heater. 

You might also need a bigger air conditioner or heater than you otherwise would if you had insulated your container. Over time, any funds saved from not insulating quickly disappears as you pay more and more energy to keep the climate in your shipping container tolerable.

To review, you will likely need to insulate your cargo container unless you live in the best possible climate. And if you choose to forgo insulation, there's a real possibility you will regret it due to all the extra money you will need to be spending on heating and cooling. You will appreciate the benefits of an insulated shipping container far more frequently than not.


One note of caution: If you don't insulate your container, not only will your home be harder to heat and cool, it may also be susceptible to water condensation, which can lead to a host of other problems such as corrosion and mold.  


Where to place your container insulation

Most building types have multiple layers of materials in their walls. The surface you see inside is not the same material as what's outside. Several layers of materials provide structure, fire resistance, weatherproofing, thermal insulation, vapor barrier, etc. 

With shipping container homes, the container itself is one such layer. And you have to decide on where the container skin will be located in the overall wall system.

The most conventional answer is to place insulation within the interior walls, inside the shipping container. These stud walls are added to most designs anyway as a place to run plumbing and electrical service and an attachment point for drywall or other interior surfaces. It only makes sense to add insulation in the cavities between the studs. Then you can more or less leave the outside of the container as-is if you want. 

However, for some people, exterior insulation is a better fit. In this case, you place insulation outside of the container and then cover that insulation with some weather-resistant sheathing. This provides the benefit of increased interior space and a more controlled exterior appearance for those who want to shield or hide the shipping containers themselves.



Factors to consider when choosing shipping container insulation

Deciding on the best insulation for your home is less straightforward than you think. Each type has pros and cons that may or may not be especially relevant to your shipping containers' specific conditions. 

We'll do our best to provide a high-level discussion of some of these criteria as we go through each type of insulation. However, know that there can be some variability depending on region and manufacturer, so always do your research.

Main factors to consider when evaluating your insulation options include:

  • Performance characteristics are affected by things like material, entrapped gas, open vs. closed-cell structure, etc.
    • R-value: How well the material prevents transmission of heat energy for a given thickness
    • Air Leakage: How well the insulation prevents air from flowing through it (which, as already discussed, is a separate but related issue from blocking heat transfer)
    • Vapor Permeability: How well the insulation prevents vapor from migrating through it and staying in it
  • Cost: Factor in both material costs and labor/equipment costs depending on if you're doing it yourself or hiring a contractor. Remember, if you're doing it yourself, ease of installation and required tools are worth considering.
  • Eco-friendliness: Many people are attracted to shipping container homes because they want to build and live in a sustainable, environmentally friendly manner. These materials vary quite a bit in the ecological impacts of their manufacture and installation.

Types of Shipping Container Insulation

There are five broad categories of insulation we're going to discuss here, grouped by the physical form they take, which is closely related to how they are applied. Much like peanut butter and peanuts might fit into two different categories of food (or applesauce and apples, or… we'll stop there!), some insulation materials may fit into more than one category below if they can be purchased and applied in different ways (we're looking at you, polyurethane foam and cellulose).  

The most important part of recognizing the differences between materials and determining how they affect your circumstances so you can choose the best type of insulation for your situation. With that said, let's jump into the different options!


Non-traditional Insulation

This insulation category comprises unconventional materials, often chosen at least in part for their eco-friendliness, and are usually considered 'cheap' insulation. Their performance makes them less suitable for most owners, given their low R-value per inch unless the eco-friendliness is your highest consideration and you're willing to sacrifice interior room for it.

While these are certainly economical forms of insulation, their practicality is not generally very high. They might be suitable for more moderate climates, where the temperature fluctuations aren't as extreme. 

  • Straw Bale: Much like the straw bale you might use to feed a horse, but instead stacked like blocks. Due to straw bales' size, this would only work for insulation on the container's exterior.
  • Hempcrete: A material similar to concrete but with less strength and made out of hemp.


Blanket Insulation

Coming in the form of insulation batts (pre-cut lengths to fit typical wall heights) and rolls (long rolled-up pieces that must be cut to length during installation), blanket insulation is somewhat "fluffy," compressible, and not self-supporting. It's much like the blanket you might use to keep warm in your house on a winter evening, except thicker and made of different materials. In almost all cases, blanket insulation makes use of long fibers mashed into a small space, effectively making it open-celled.

Blanket insulation is intended to be fastened in the cavities between studs and uses those studs for structural rigidity since it will just fall over into a pile without support. It is one of the cheapest options and is very easy to install, typically requiring a stapler to fasten to studs.

Varieties of blanket insulation include:

  • Fiberglass Insulation: Made from superheated sand or recycled glass that is spun into thin fibers. In western countries, this is the most common type of cheap wall insulation.
  • Slag Wool, Mineral Wool, and Rock Wool Insulation: Similar to fiberglass, but made from minerals/ceramics, or 'slag,' a byproduct of metal production
  • Sheep Wool Insulation: Just like it sounds, insulation made from the sheared wool of sheep
  • Cotton or Denim Insulation: Made from cotton, often with a blue-ish color, as much of it is sourced from recycled denim or blue jeans. Pricier, but with a very high percentage of recycled contents

Blanket insulation is quite permeable to water vapor, mitigated with a vapor retarder in traditional construction. However, as discussed in our condensation article, vapor retarders are usually not good choices for container homes because the outer metal skin is already a vapor barrier itself. Adding a second barrier, you can end up trapping water vapor in the wall cavities.

Some of the fibers used to make blanket insulation, most noticeably fiberglass, can be irritating to the eyes, skin, and respiratory systems. Proper PPE (personal protective equipment) such as a dust mask, gloves, and safety glasses is necessary before handling these materials. Consult the MSDS (Material Safety Data Sheet) or other product packaging instructions for proper handling procedures.



Loose-Fill Insulation

This insulation type is based on applying small macroscopic (easily viewable with the naked eye) chunks of insulating media into a wall cavity. These insulators generally require complete wall cavity containment before application. Otherwise, you'll have a pile on your floor.

  • Cellulose Insulation: Made from recycled paper that is shredded, then blown in by a machine
  • Loose-Fill Fiberglass Insulation: Similar to fiberglass batts, but less dense and not tightly bound so that they can be blown in by machine
  • Vermiculite Insulation and Perlite Insulation: Minerals that have been heated and expanded like popcorn, creating a sort of natural foam pellet that can be added to wall cavities

Given their vapor permeability, loose-fill insulation materials aren't recommended for containers.



Expanded Foam Insulation

Expanded foam is made offsite into large boards and insulation panels that are pre-sized for standard wall heights. Unlike blanket insulation, these insulation panels are self-supporting. Holes for things like doors and windows are built on-site by cutting. Like spray foam insulation, the gas in closed cell expanded foam variants can sometimes escape the cells and cause a reduced R-value over time.

Expanded foam is DIY-friendly and can be fastened to studs or even glued right to the container. It can be rather quick to install unless you have a lot of cuts to make. Some varieties are formed to match the corrugations of a shipping container wall. If not, you'll have large air gaps in these corrugated areas.

In most cases, expanded foam insulation has the greatest R-value per inch of all insulating materials discussed in this article.

  • Open Cell Polyurethane Foam Insulation (of PU Foam): Open-cell foam cells are not as dense and are filled with air, which gives the insulation a spongy texture and a lower R-value.
  • Closed Cell Polyurethane Foam Insulation (cc PU Foam): The 'blowing agent' fills the tiny microscopic cells with a gas other than air that has better heat conduction properties, increasing the R-value of the foam
  • Extruded Polystyrene Foam Insulation (EPS): Composed small plastic beads fused into a closed-cell foam. It's the white foam you're familiar with seeing in the form of things like coffee cups, and it's what the shipping container insulation kits from companies like InSoFast are made of.
  • Expanded Polystyrene Foam Insulation (XPS): Begins as a molten material that is pressed out of a form into closed-cell foam sheets. While the name is similar to EPS, it's quite a bit different.
  • Polyisocyanurate (Polyiso): Similar to polyurethane, but with more rigidity


Spray Insulation

Spray insulation can be created from several materials applied by spraying or pumping out a liquid mixture that then hardens into a solid. It is applied and adheres to itself; spray insulation is continuous and expands into nooks, crannies, and cracks. This forms a barrier that holds air movement as well as the transference of heat.

Spray foam insulation expands upon application then hardens, which helps further with sealing. However, it does need trimming as the expansion will push the foam past the face of your studs.

  • Open-Cell Spray Polyurethane Foam (SPF): The less desirable type of polyurethane spray foam insulation, as it has a lower R-value per inch due to air movement allowance between cells. 
  • Closed-Cell Spray Polyurethane Foam (SPF): The most common shipping container insulation and recommended for most owners. This type of spray foam insulation gives one of the highest R-values per inch and forms a nice vapor retarder. There is some concern with off-gassing after spray application, so be sure to check with your manufacturer about cure times and how long to wait before occupancy. The gas in these closed-cell variants can seldom escape the cells and cause a reduced R-value over several years.



A separate but related option is non-expanding sprayed-in insulation. Unlike the spray foam insulation types above, it doesn't chemically expand upon application, but it does move about to fill up the cavity.

  • Damp-Spray Cellulose Insulation: Made from recycled paper products that are shredded. As opposed to the typical blown-in application, a special rig can be used that adds water or adhesives at the point of application (called damp-spraying), which binds the cellulose together and enables it to be applied to open-sided wall cavities.
  • Cementitious Foam Insulation: An extremely light mixture of water, air, and natural minerals that resembles concrete when cured, but shaving cream when first applied and can be a bit crumbly after curing if you aren't careful with it. However, thanks to its ingredients, cementitious foam is eco-friendly, non-toxic, and non-flammable despite lagging spray foam insulation in R-value.

As you can see, the options available are quite extensive. Choosing the best insulation for you needs a proper understanding of your own decision making factors, like budget, climate, design, and personal tolerance to hot and cold.

If you doubt, take a look at what people in your geographic area are now doing. It's often easier and cheaper to use materials that are already common for your region. A conversation with a local construction contractor to get site-specific recommendations and advice may also be useful.




Refrigerated Shipping Containers

The bulk of this article comes from the position of adding insulation to a traditional shipping container. However, another option is purchasing an insulated shipping container used to carry cold products like flowers and produce. There are many pros and cons to this option, but it can be a good choice if you can find these containers at a reasonable price.



Other Thermal Energy Control Ideas That Aren't Really "Insulation."




Green Roof

A green or living roof is a rooftop garden of sorts made with different grasses and other plants. Soil and plants aren't great insulators, but they can block solar radiation if you live in a warm climate. Therefore, a green roof isn't a replacement for more conventional insulation forms but a supplement to it.

An additional benefit of green roofs is that they look great! From the sky, your container home will look like just another patch of ground. And while it's not a great option for insulation, it's still an environmentally-conscious option and does add an element of protection.




Reflective/Radiant Barriers

While the other types of insulation discussed above work to slow the transmission of heat energy via conduction (and to a lesser degree convection), we still have radiation to consider. As you know from our article on heat transfer in shipping container homes, radiation is the least understood heat transfer form, but it's still incredibly important in shipping container homes.

Unless you're open to lining your container with a mylar space blanket like the ones commonly carried by hikers, getting a radiant barrier will likely include a coating of some sort. Be careful to notice the difference between paint and coatings created to reflect and emit radiation energy. 

Coatings are specially formulated to reflect the unseen infrared light of thermal energy, and though they may look similar to paint, they work much differently.




Passive Heating and Cooling Design

Another possibility is designing your home in such a way that it minimized the amount of energy needed to heat and cool it. Various methods attempt to achieve this, which are beyond the scope of this article. Examples include Trombe Walls, Solar Chimneys, and others. The effectiveness of these techniques changes dramatically based on your climate.

While these passive methods can be effective in more temperate climates, they often won't be enough on their own. For instance, the coolest you'll ever feel in a passive-designed container is if you were standing outside in the shade with a breeze blowing. If even that is too hot, a passive design isn't going to be enough.


As you might have guessed, a common theme running throughout this article is the vast number of options available for shipping container home insulation. But always remember that insulation is just one part of a broader plan and building design.

You need to consider container home insulation in the context of your overall needs and architectural ideas. It has to be a consideration from day one, as it affects almost every later decision. It also needs to fit into your overall budget and account for factors such as climate, ease or difficulty of installation, size of the build, personal preference, and more.


By understanding the realities of financial resources and physics, plus managing your expectations surrounding things like interior comfort, you'll end up with a project you love! So start early and develop a clear vision for your shipping container construction dream.


Summary

You have quite a few insulation options at your disposal, and what you choose is driven by factors like your climate, design, and budget. All choices have their pros and cons, but now you fully understand what those are.

One thing to keep in mind is that you don't necessarily have to use a certain type of insulation solely. For instance, you could use closed-cell polyurethane spray foam insulation for the container walls and roof and then use rock wool blankets underneath the container to keep the cost down.

You can even mix insulation in the same area. For example, you could use rock wool underneath the container and then spray an inch of closed-cell polyurethane foam over the rock wool to create an airtight seal. Whatever you do, make sure you understand the implications of condensation if you're in a climate where it is a concern.


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