What do grape stalks, pineapple leaves, corn cobs, rice husks, sheep’s wool, and straw have in common? Apart from being natural materials, they have all been used to insulate homes. Increasingly, people are turning towards natural, sustainable materials as climate change and waste have become bigger problems.

Existing building insulation materials such as synthetic rock wool are excellent at keeping our homes warm in winter, but the conversation has moved beyond thermal performance. Energy use, re-usability, toxicity, and material disposal are all live considerations now, especially with regulations and emissions targets tightening. So, rock wool might perform better than straw bale insulation but straw is biodegradable, reusable, easy to disassemble, and doesn’t require large amounts of energy to process.

Sheep’s wool and hemp insulation have also become attractive to homeowners and housebuilders alike, but an even more encouraging prospect is the use of waste materials to create next generation insulation. In this spirit, researchers at Flinders University in Adelaide, Australia, have taken waste cooking oil, wool offcuts, and sulphur to process a novel housing insulation material.

Recycled paper is one of many waste materials that has found its way into domestic insulation.

To make this composite, they followed several stages. In the first stage of the synthesis, the researchers used inverse vulcanisation to create a polysulphide polymer from canola oil triglyceride and sulphur. They then mixed this powdered polymer with wool and coated the fibres through electrostatic attraction. This mixture was compressed through mild heating to provoke S−S metathesis in the polymer and bind the wool. The wool bolsters the tensile strength of the material, makes it less flammable, and provides excellent insulation. The result is a sustainable building material that fulfils its function without damaging the environment.

For Associate Professor Justin Chalker, the lead author of this study, this work provides an ideal jumping-off point. “The promising mechanical and insulation properties of this composite bodes well for further exploration in energy saving insulation in our built environment,” he said.

Sustainable transformation

It is clear that ventures like the one in Adelaide will continue to sprout all over the world. After all, necessity dictates that we change the way we build our homes and treat materials.

A recent report from Emergen Research predicts that the global insulation materials market will be worth US $82.96 billion (£59.78 billion) by 2027. The same report was also at pains to mention that the increasing demand for reduced energy consumption in buildings will be a significant factor in influencing industry growth.

“Market revenue growth is high and expected to incline rapidly going ahead due to rising demand for insulation materials... to reduce energy consumption in buildings,” it said. One of the main reasons given for this increased green building demand was stricter environmental regulations.

And Emergen isn’t the only organisation feeling the ground moving. Online roofing merchant Roofing Megastore, which sells more than 30,000 roofing materials, has detected a shift towards environmentally friendly materials, with many homeowners sourcing these products themselves.

Rock wool insulation panels have come under greater scrutiny in recent times.

Having analysed two years of Google search data on sustainable building materials, the company found that synthetic roof tiles are generating the most interest from the public. Like the Flinders insulation, these roof tiles make use of waste materials, in this case recycled limestone and plastic. And you don’t need to look far down the list to find sustainable insulation materials, with sheep’s wool insulation in 9th place, wood fibre insulation in 10th, and hemp insulation in 12th.

Over time, the logic of the progression towards natural, less energy-intensive building materials will become harder to ignore. “Traditional materials such as synthetic glass mineral wool offer high levels of performance but require large amounts of energy to produce and must be handled with care while wearing PPE,” the company noted. “Natural materials such as hemp or sheep’s wool, however, require very little energy to create and can be installed easily without equipment.”

So, the next time you look down at your nutshells, spent cooking oil, or tattered woollen sweater, think of their potential. In a few years, these materials could be sandwiched between your walls, keeping you warm all winter.

Insulating composites made from sulphur, canola oil, and wool (2021): https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202100187?af=R