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Blow-In Fiberglass That Sticks Like Glue

Originally developed as an alternative to damp-spray cellulose, Johns Manville Spider Custom Insulation is a unique spray-applied fiberglass product that’s manufactured using 25 percent recycled content. Unlike cellulose, which needs plenty of water to adhere to cavity walls, Spider gets sticky with only a light misting of adhesive. It requires no open-cavity drying time, so drywallers can start hanging board as soon as the insulators have packed up and moved on.


According to JM research engineer Francis Babineax, the insulation adheres to vertical surfaces “like a spider” because its glass fibers are much finer (less than 2 microns in diameter) and more flexible than the 4- to 5-micron fibers that make up conventional insulation. These miniscule fibers clump together to form BB-sized “nodules,” the bundled fibers that give fiberglass insulation its air-trapping ability. “We’ve known for some time that a finer fiber would give you great thermal and acoustic performance,” he says. “And when provided as small nodules, these fiber bundles have the ability to easily fill complex cavities and hold together far better than larger ones.”

Because of its adhesive qualities, Babineax adds, Spider can be sprayed overhead (between floor joists or rafters, for example) without the need for netting, and it will never settle, no matter where it’s applied. He says that the insulation offers a unique advantage for closed-cavity fills because the tiny nodules can pass through a hose as small as 1/2 inch in diameter. Some installers, he says, have successfully insulated brick houses by drilling through the mortar joints.

Babineax also claims that Spider’s tiny, flexible fibers are significantly less itchy and dusty than conventional fibers.

Spider is designed to be compatible with existing fiberglass blowing machines. According to the maker, it has an R-value of 4.2 per inch and must be installed by a certified contractor. Installed costs are comparable to those for cellulose and at least 30 percent less than for open-cell foam. For more information visit

High-Tech Gaskets

Not too long from now, the hottest insulation on the market might be something you’ve never heard of: aerogel. This high-tech material is made of granules of silica that — to put it simply — have had the moisture sucked out of them, creating tiny “nano-bubbles” that are little more than cell walls and air (95 percent air, in fact). Trapping air on a microscopic level such as this gives aerogel a huge R-value (as much as 10.3 per inch) and an equally huge price tag. For years NASA has used aerogel to insulate space shuttles and the Mars lander against the extreme conditions of space. Now a number of manufacturers are working on ways to make aerogel insulation cost-effective for buildings.


“Aerogel is the highest insulating material ever known, and it couldn’t be better for the environment because it’s almost entirely made from sand,” says Lahnie Johnson, president of Acoustiblok. His company gets around the cost barrier by producing aerogel in thin strips that function as thermal blockers rather than insulation. Thermablok Thermal Strip Insulation is a 1/4-inch-thick by 1 1/2-inch-wide peel-and-stick membrane that’s applied between framing members and the drywall, or beneath the sheathing.

According to Johnson, testing performed at the DOE’s Oak Ridge National Laboratory in Tennessee has shown that Thermablok reduces energy loss by 38 percent when used with metal framing and 19 percent when used with wood framing. He says that the thermal blocking capability of the skinny material is roughly equivalent to that of a 1 1/2-inch-thick layer of rigid foam. He also claims that the strips are completely unaffected by moisture and will not off-gas or degrade over time.

Thermablok Thermal Strip Insulation has been on the market since the middle of last year. The manufacturer is working with the federal government to qualify the material for energy-conservation tax credits. It’s sold in 4-foot-long strips and can be ordered directly from the manufacturer ( for $0.98 per lineal foot.

Tom O’Brien is a freelance writer and carpenter in New Milford, Conn.