Hemp vs Sheep wool insulation | Everything you need to know

January 21, 2021

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4 min read

Hemp wool and sheep wool are considered to be the “greenest” or most sustainable insulation materials. In this video, we’re going to look at how they are made, their main differences as well as their pros and cons.

HempWool Insulation by Hempitecture

Before we address any misconceptions, rest assured that this product will not induce any psychoactive effects. Industrial hemp contains less than 0.3% THC (tetrahydrocannabinol), which is the psychoactive component of cannabis. Hemp is a versatile plant used to produce various products like oil, paints, animal feed, soap, and lotions. For insulation, we focus on the stalk, which comprises two layers: the inner hurd or shiv, used for hemp blocks, hempcrete, and paper, and the outer bast fiber, historically used for ropes, clothing, canvas, sails, and now Hemp wool insulation batts.

To create Hemp wool, long and robust fibers are separated from the bark, combed to remove any hurd particles, and then compressed to form batt insulation products. Hempitecture’s Hemp wool is composed of 92% industrial hemp fiber and 8% textile polyester binder. The insulation is available in batts and rolls due to the tough, intertwined nature of the fibers, preventing it from being used as loose-fill.

Sheep wool insulation by Havelock

After sheep shearing, the wool is sorted based on color and then washed to remove dirt, vegetable matter, and grease. Once dry, the wool is combed to align the fibers in one direction. Multiple wool layers are created using a pendulum that swings back and forth, and these layers are bonded using a needle punch to stitch them together.

Havelock sources all their wool from New Zealand, where strict animal welfare regulations govern sheep treatment. New Zealand’s sheep outnumber humans 6 to 1, ensuring ethical practices. Havelock offers both loose-fill and batt insulation. Batt insulation is easier to install, but over time, it can slump, unlike loose-fill, which retains its shape.

R Value

Both Hemp wool and sheep wool exhibit similar performance. A 2-inch deep batt has an R-value of 7, while a 5.5-inch batt is R20 for both materials. Pricing-wise, they are surprisingly similar, with 5.5-inch thick Hemp wool priced at $1.95 per sqft and the same thickness of sheep wool costing $2.25 per sqft.

Dimensional Stability

Both materials rely on trapped air for insulation, but Hemp wool boasts greater stiffness, density, and dimensional stability. It can hold more trapped air and is tightly woven, bouncing back to its original shape after compression. On the other hand, sheep wool is softer, malleable, and lightweight, but its dimensional stability is inferior to hemp wool, potentially leading to higher thermal drift.

Sound, water and fire repellency

A unique quality of sheep wool is its ability to serve as a sound absorber, with an NRC rating of 0.9, indicating that it absorbs 90% of sound.

Water repellency tests revealed that both materials absorb water without disintegrating, making them vapor permeable and hygroscopic, maintaining moisture control and resisting mold and mildew.

However, the fire test revealed a concerning result for untreated Hemp wool, which caught fire easily and released acrid smoke and fumes. Sheep wool, though singed, did not spread the flame. Treating Hemp wool with fire and flame retardants may be necessary, as with Hempcrete, which exhibits fire retardant properties.

Environmental aspects

Hemp wool and sheep wool shine as environmentally friendly insulation choices. Hemp plants require minimal water for growth and processing, making them more water-efficient than cotton. With a quick turnaround time of as few as 70 days from planting to harvest, hemp is a sustainable resource. Additionally, it requires no insecticides or pesticides and contains no VOCs, making it safe to handle without gloves, masks, or eye protection.

Similarly, sheep wool offers impressive eco-friendly features, boasting the least embodied energy of all insulation materials, making it an environmentally responsible choice. After its life cycle, sheep wool can be used as fertilizer or compost, further reducing waste.

Conclusion

In conclusion, both hemp wool and sheep wool present excellent eco-friendly insulation alternatives. Hemp wool’s dimensional stability and sheep wool’s fire-retardant properties make them stand out. As more companies enter this sector, the costs are likely to become more competitive with traditional insulation options.