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 just stop there!) some insulation materials may actually fit into more than one category below if it 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 personal 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 category of insulation is made up of materials that somewhat unconventional, often are 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 the size of straw bales, this would only work for insulation on the exterior of the container
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 only 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 from ‘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, which in traditional construction rentcontainer can be mitigated with a vapor retarder. However, as we 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, and by 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 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 instructions on the product packaging for proper handling procedures.
Loose-Fill Insulation
This type of insulation 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 prior to application, otherwise, you’ll just have a pile on your floor.
Cellulose Insulation: Made from recycled paper products that are shredded, then blown in by machine
Loose-Fill Fiberglass Insulation: Similar to fiberglass batts, but less dense and not tightly bound so that it can be blown in by machine
Vermiculite Insulation and Perlite Insulation: Minerals that have been heated and expanded like popcorn, making a sort of natural foam pellet that can be added to wall cavities
Given their vapor permeability, loose-fill insulation materials aren’t really recommended for containers.
Expanded Foam Insulation
Expanded foam is manufactured offsite into large boards and insulation panels that are pre-sized for typical wall heights. Unlike blanket insulation, these insulation panels are self-supporting. Holes for things like doors and windows are made on-site by cutting. Just like with 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 attached to studs or even glued right to the container. It can be pretty quick to install unless you have a lot of cuts to make. Some varieties are molded to match the corrugations of a shipping container wall. If not, you’ll have large air gaps in these corrugated areas.
Expanded foam insulation in most cases has the highest R-value per inch of all insulating materials discussed in this article.
Open Cell Polyurethane Foam Insulation (oc 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 of small plastic beads that are fused container workshop to rent together into a closed cell foam. It’s the white foam you’re familiar 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 made out of several materials that are all applied by spraying or pumping out a liquid mixture that then hardens into a solid. Due to how it is applied and adheres to itself, spray insulation is continuous and expands into nooks, crannies, and cracks. This forms a barrier that resists 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 require trimming as refrigerated container for rent the expansion will push the foam past the face of your studs.
Open-Cell Spray Polyurethane Foam (ocSPF): The less desirable type of polyurethane spray foam insulation, as it has a lower R-value per inch due to the allowance of air movement between cells.
Closed-Cell Spray Polyurethane Foam (ccSPF): The most common shipping container insulation, and what we recommend for the majority of owners. This type of spray foam insulation provides 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 sometimes 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 around to fill up the cavity completely.
Damp-Spray Cellulose Insulation: Made from recycled paper products that are shredded. As opposed to the Special container normal 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 refrigerated containers for rent is eco-friendly, non-toxic, and non-flammable despite lagging behind spray foam insulation in R-value.
As you can see, the options available are quite extensive. Choosing the best insulation for you really requires a proper understanding of your own decision making factors, like budget, climate, design, and personal tolerance to hot and cold.
If you are in doubt, take a look at what people in your geographic area are already 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.