Insulation R-Values
- Posted
Hive insulation is a question that often pops up and I thought it might be a useful tool to provide R-values and other details about insulation that would be helpful to beekeepers considering this topic either for added winter preparation or hive construction. All the information below has been collected for you from institutional or product sites on the web and I will include the sources in the referenced material section at the bottom if you want to dig in a little deeper before making a decision. A discussion on insulation, as you might expect, includes a number of additional topics such as moisture, reflected radiation, thickness, compression impacts, aging, etc. I will try and mention as many additional considerations as possible to help you see the differences in your future insulation solution.
At the start of the 20th century insulation may not have been a significant topic for most beekeepers. In the US many thought the ¾” pine walls of their hives provided everything the bees needed to survive the winter but those in the 19th century and earlier used solutions common to their agricultural lifestyle. Clay, straw, manure, willows, sheds, niches in southern facing walls, and trenches were all used to protect their bees from the winter punishment. Resent thermal dynamic research on the hive interior, increasing annual colony failure, pests and pest management impacts, and significant migratory stress in the US has encouraged more beekeepers to consider insulation as an import part of their winter management practices.
Natural but significant climatic changes caused by the El Niño and La Niña (opposite phases) climate patterns known as the El Niño-Southern Oscillation (ENSO) has also impacted our local weather and can cause unexpected years of seasonal variations to local precipitation and temperature. This can also change what was once an unimportant beekeeping management practice into something critical in the present. Everyone has particular weather conditions specific to their local area which along with ENSO impacts can also be affected by local geography (rivers, mountains, plains, farm land, woodland, lakes, oceans, etc). Weather conditions are particular to each beekeeper.
Beekeepers should consider their local and specific geographical conditions when developing what insulation solution to use. We should also remember that old solutions may not be appropriate now that we know more about our bees, what is happening inside the hive, and can better forecast our weather. Providing insulation should meet our bees needs and create the best solution and not just what “might” just get them through the winter. If we are going to do the work, we should do the best we can verse the least. More won’t hurt but less just might.
Common Insulation Solutions
Each material you consider has specific insulative qualities. Below are the basic R-Values and additional details for each. Remember that R-Value is how strongly a material resists heat flow. Conduction is heat transfer through direct contact between particles—for example, heat moving through a wall’s solid materials (or insulation). An insulation material’s R-value measures how much it resists heat flowing through it. The greater the R-Value the slower the transfer and slower the conduction.
When discussing “Cold” keep in mind that it isn’t something that transfers; heat moves from warmer places to cooler ones. So, when people say cold is transferring through insulation, they usually mean heat is leaving the warmer side and moving toward the colder side. Insulation slows the heat flow and, in our situation, gives the bees more time to respond and modify their interior conditions without quickly turning to extreme or emergency responses until absolutely required.
Reflectix:
| Property | What to expect |
| Common Use | Beekeepers often use this material in situations where its important to have something resistant to bees chewing, easy to remove or peel off if propolised, and/or when the heat from the colony needs to be reflected back into the colony. |
| R-value | It has a limited R-value of its own. It’s a reflective insulation or a radiant barrier which depends mainly on the enclosed air space and direction of heat flow. With no air space between layers, the manufacturer says the added benefit is minimal—about R-1.1 per layer for its double-bubble product. |
| Moisture permeability | It is designed to resist moisture rather than absorb it, and the manufacturer describes it as a vapor/moisture barrier in certain assemblies. Still, seal seams and edges as the installation instructions specify, and don’t treat it as a substitute managing condensation. |
| Compression impact | This can affect Reflectix’s performance if it squeezes out the air space. Its reflective insulation performance depends mainly on an enclosed air space next to the reflective surface; with no air space, the added benefit is minimal. |
| Age impact | Age alone usually doesn’t noticeably reduce Reflectix’s performance if it has stayed dry, intact, and installed correctly. Over time, though, physical damage, delamination, torn seams, UV exposure, or a lost/blocked air space can reduce how well the assembly works. |
Asphalt-saturated felt roofing paper (traditional tar paper):
| Property | What to expect |
| Common Use | Often beekeepers wrap their hives in the winter with this paper to increase radiant heat absorption and to cover hive part gaps. |
| R-value | Very low—roughly R-0.1 per layer as a practical estimate. It is underlayment, not insulation, and shouldn’t be counted on for meaningful thermal resistance. |
| Moisture permeability | It sheds liquid water when properly installed, but it is not completely vapor-impermeable. Reported vapor permeance varies widely; a commonly cited range is about 0.56–6 perms when dry, and it can become more permeable when damp. |
| Compression impact | Compression does not provide a useful insulation benefit. Felt is thin, so compression usually matters more if it causes wrinkles, tears, punctures, or disrupted laps that let water through. |
| Age impact | Aging can make felt brittle, fragile, or more moisture-absorbent, especially after prolonged exposure to sun, heat, weather, or repeated wetting. Under intact roofing it is protected, but age and condition still matter; replace it if it is brittle, torn, or deteriorated. |
- The “R-value” estimate is only approximate; roofing felt is generally selected for water-shedding and roof-system compatibility, not insulation.
Raw Wool:
For raw sheep’s wool, there isn’t one dependable insulation rating: performance varies with its cleanliness, density, thickness, and how it’s used in the insulation solution.
| Property | What to expect |
| Common Use | Beekeepers are commonly using wool as an insulation material in the walls and roofs of a custom-built hive often because they can get it free or at a price much cheaper than other insulation materials. |
| R-value | Prepared wool insulation is roughly R-3.5 to R-4 per inch. Raw fleece has no standardized R-value. Dirt, sweat (suint), plant matter, and excess grease can make the fleece denser or clump it unevenly, changing the amount and distribution of trapped air—the main source of its insulation. That can make performance less consistent, but there’s no dependable rule like “cleaner wool has a higher R-value.” Raw fleece has no standardized R-value; it depends on thickness, density, loft, and installation. |
| Moisture permeability | Wool is vapor-permeable and absorbs/releases water vapor. It can hold moisture without immediately feeling wet, but it is not a water barrier; bulk water or prolonged dampness still needs to be addressed. Dirt and suint can attract or hold moisture and may contribute to odor or biological deterioration. Lanolin—the wool’s natural grease—helps repel liquid water, but it doesn’t make wool waterproof or prevent it from absorbing water vapor. Washing out lanolin may reduce that water-repellent effect; it doesn’t necessarily make the wool more vapor-permeable in a simple, predictable way. |
| Compression impact | Packing or compressing wool changes its thickness and density, so its total R-value may fall when it occupies less space. Avoid over-packing; install to the product’s specified density and thickness. |
| Age impact | Properly installed wool insulation can last for decades, but raw, untreated wool is vulnerable to insects, and dampness, pests, or settling can affect performance. Prepared insulation may include pest treatments and stabilizing fibers, so its durability depends on the product. |
- Raw fleece isn’t necessarily suitable for a building cavity as-is. It may need cleaning and pest treatment, and its performance can’t be assumed to match tested insulation batts. This is not to say that historically raw wool hasn’t been successfully used as an effective insulation solution when others are not available.
Wood (3/4” Pine Board):
| Property | What to expect |
| Common Use | This is the common thickness of most US built or purchased hive walls and lids. Some custom hives may use 1-1/2 thick pine in the their walls for the 2X the R-value but this dramatically increases the product weight. |
| R-value | About R-0.8 to R-1.1 for ¾ inch of dry pine. Pine is structural wood, not high-performance insulation. Published values vary by species and test conditions. |
| Moisture permeability | Vapor-permeable, but the exact permeance varies substantially with pine species, moisture level, grain, and finish. Paint or coatings can reduce vapor movement; bare wood can also absorb liquid water, so it isn’t a moisture barrier. |
| Compression impact | Ordinary light compression has little effect, since solid pine doesn’t work like fluffy insulation. Heavy loads can crush or permanently deform the wood, potentially opening gaps or damaging the assembly. |
| Age impact | If kept dry and protected, pine can remain serviceable for a long time. Repeated wetting, rot, insects, or weathering can weaken it and affect thermal performance; moisture in the wood also lowers its insulating value. |
Denim Insulation
| Property | What to expect |
| Common Use | Beekeepers are using this type of insulations as a more natural alternative to rigid foam boards in the walls of insulated hives. |
| R-value | About R-3.5 per inch is a commonly reported average. Actual labeled R-value varies by product and batt thickness; for example, R-13 in a 3.5-inch batt works out to about R-3.7/in. |
| Moisture permeability | Denim is a fibrous insulation. A reliable, general perm rating was not found that applies across denim products. Permeance depends on the specific product, thickness, and test method. Vapor permeance is not the same as resistance to liquid water: denim can absorb water, become heavy, pack down, and dry slowly. |
| Compression impact | Avoid compressing it. Squeezing batts into undersized cavities reduces thickness and can lower thermal performance. Some shipping-compressed batts may not fully recover their original loft; check the product instructions and fit batts snugly without stuffing them. |
| Age impact | The practical long-term concerns are keeping it dry and maintaining its loft: moisture or persistent compression can impair performance. |
Rigid Foam Board:
There are four primary types of foam board insulation, each with distinct characteristics that make them suitable for various construction applications.
- EPS — Expanded polystyrene
- XPS — Extruded polystyrene
- ISO (polyiso) — Polyisocyanurate
- NGX — Owens Corning’s extruded polystyrene (XPS) insulation. It is a reformulated version of XPS designed to have a lower environmental impact. NGX uses a blowing agent with significantly reduced global warming potential compared to traditional XPS.
| Property | What to expect |
| Common Use | Beekeepers are using this rigid foam board insulation to wrap hives for the winter and within walls and lids for fully insulated hives year around. |
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| Moisture permeability |
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| Compression impact | Compression can reduce effective R-value if it permanently reduces the foam’s thickness |
| Age impact |
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| Cost |
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| Application |
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- Choosing the right type of foam board insulation depends on your specific needs, including budget, climate, and application requirements.
Reference Material
- Reflective Technology Performance Information
- Comparing Asphalt Felt and Synthetic Underlayments
- Pros and Cons of Sheep’s Wool Insulation for Homes
- History of Wool Insulation
- Know the R-Value of Wood for Energy Efficient Log Home
- Permeability of Common Building Material to Water Vapor
- Is Wood a Good Insulator? Understanding Thermal Conductivity and R-Value
- Insulation Comparison: Rigid Foam Insulation Types
- Denim Insulation: The Good And The Bad