Natural fiber insulation materials have gained renewed attention as builders and homeowners seek alternatives to petroleum-based and mineral insulation products. While they typically cost 2 to 4 times as much as conventional fiberglass, natural insulations offer unique performance characteristics including moisture buffering, low embodied carbon, and simplified handling without protective equipment. The five principal natural insulation materials are sheep wool, hemp, wood fiber, cotton/denim, and cork.
Sheep Wool Insulation
Sheep wool insulation achieves R-3.5 to R-4.0 per inch, comparable to mineral wool. Its most distinctive property is strong hygroscopic behaviour: wool can absorb up to 35 percent of its own weight in moisture without feeling wet or losing insulating performance. This moisture buffering helps regulate indoor humidity by absorbing water vapour when relative humidity is high and releasing it when the air dries. The natural lanolin content of wool provides some resistance to insects and mild flame retardance, though commercial wool insulation products add borate treatment to meet building code fire requirements.
Major brands include Havelock Wool, a New Zealand and US company sourcing wool from sheep raised in New Zealand, and Thermafleece, a UK brand that blends sheep wool with recycled fibres for batts and rolls. Sheep Wool Insulation Ltd supplies the European market with products manufactured in the UK and Ireland. Wool insulation is sold in batt and roll form, installed similarly to mineral wool, and can be handled without gloves or respiratory protection.
Hemp Insulation
Hemp insulation, with an R-value of approximately R-3.5 per inch, is produced from the woody core fibres of the industrial hemp plant. Because hemp grows rapidly and sequesters significant carbon dioxide during its growth cycle, hemp insulation is considered carbon-negative at the point of manufacture. The fibres are treated with a soda-based fire retardant and bonded with a small percentage of polyester or cornstarch binder. Hempitecture, based in the United States, produces HempWool batts sourced in part from domestic hemp growers. European manufacturers have produced hemp insulation batts since the 1990s, and the material is well established in France, Germany, and the UK.
Wood Fiber Insulation
Wood fiber insulation boards, produced primarily in Germany by Gutex and Steico, are made from softwood chips that are pulped and formed into rigid boards through a wet-process method that uses the wood's natural lignin as a binder. Wood fiber achieves R-3.5 per inch and is particularly valued for exterior continuous insulation applications, where interlocking tongue-and-groove boards create a monolithic insulating layer with good summer heat protection due to the material's relatively high thermal mass. Steico and Gutex products are widely used in European Passive House construction as an alternative to foam-based exterior insulation.
Cotton and Denim Insulation
Bonded Logic UltraTouch is the best-known cotton-based insulation in North America. It contains 80 to 85 percent post-industrial recycled denim fibres, primarily scrap from denim manufacturing, with the remaining 15 percent comprising a polyester binder and borate fire retardant. UltraTouch achieves R-3.7 per inch and is sold in batt form for standard wall and ceiling framing. Like sheep wool, it can be handled without protective gear, which makes it popular for DIY installations and for use in homes where occupants have chemical sensitivities.
Cork Insulation
Expanded cork insulation boards are produced from the bark of the cork oak tree, which regenerates after harvesting, making cork a renewable resource. Amorim Insulation, a division of the Portuguese cork giant Corticeira Amorim, produces expanded cork boards with an R-value of approximately R-3.5 per inch. The boards are manufactured by superheating cork granules in autoclaves, causing the natural suberin resin to expand and bind the granules together without added adhesives. Cork insulation is naturally fire-resistant, rot-resistant, and dimensionally stable, and is used primarily in exterior insulation systems in European construction.
Cost Considerations
Natural insulation materials typically cost 2 to 4 times as much as conventional fiberglass batts per unit of R-value. Sheep wool is generally the most expensive, followed by cork and wood fiber, with cotton denim and hemp occupying the middle tier. The premium reflects smaller production volumes, more labour-intensive manufacturing, and the absence of the economies of scale enjoyed by the fiberglass and foam industries. Builders choosing natural insulation often do so for sustainability certifications, healthy indoor air quality goals, or specific moisture-management performance rather than on a first-cost basis.