Foil-Backed Fiberglass Insulation Installation

Updated February 21, 2017

Foil-backed insulation products have gained popularity as homeowners experiment with passive solar techniques and the nation emphasises energy conservation. Radiant barriers are made of aluminium foil that is a tremendous radiant energy blocker but a terrible conductor, so it doesn't transfer heat to other materials. Installing these reflective foil insulation products in conjunction with traditional fibreglass insulation can lower energy bills and make homes more comfortable in extreme weather.

Types and Uses

Reflective foil products are trusted by NASA to block free radiation in space to protect astronauts during spacewalks. Without it, there wouldn't be an International Space Station. Here on earth, plastic sheeting coated with reflective foil (usually polished aluminium) protects homes from the radiant energy of the sun. When installed with the shiny side out, 85 per cent of the sun's heat is blocked, while the nonconductive material prevents reradiation of that heat into the home. There are also roof decking (the sheathing under shingles) products that are reflective for use in new construction and redecking projects.

Fibreglass insulation blankets are often backed with paper or foil. This is a vapour barrier, and it also serves to keep needed heat in the home in the winter. Foil-backed fibreglass insulation can be used in conjunction with radiant barriers to provide complete protection, blocking unwanted summer heat and retaining the needed winter warmth from inside.


The reflective barriers work best when the reflective surface is closest to the heat source. In hot climates, staple sheets of foil barrier directly to the roof trusses or rafters in the attic with the shiny side facing the roof. Tim Carter at Ask the Builder recommends leaving a small gap at the top and the bottom of the sheet to accommodate any moisture build-up. Changing temperatures can cause moisture in the air to condense on the foil; leaving the gaps allows it to escape and evaporate.

Foil-backed fibreglass, on the other hand, should be installed between joists with as few gaps as possible. The fibreglass should always be flush to the outside wall with the foil or paper backing facing in. Always cut around wiring and pipes so that there is a continuous barrier of fibreglass against the wall. Insulating over obstructions without cutting it in behind them leaves gaps, and even small gaps can sap the benefit you get from the rest of the properly done job.

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