Should foil insulation be shiny side in or out?

Author: Stacy McCullough  |  Last update: Wednesday, December 10, 2025

If you are wondering how to install the foil backed insulation on your walls here you have few tips to consider. if it is hot outside, the reflective part of your foil insulation must face outside. if it is freezing outside, the best orientation of the reflective part is inside.

Should the shiny side of foil be up or down?

While aluminum foil has a dull and shiny side, there is no difference in how either side reflects heat.

Should silver side of roof insulation go up or down?

Installing it

No air space means no thermal value. The reflective side must be facing downwards when in roofs, upwards when installed underneath a floor and inwards when installed in walls.

Which way does foil insulation go?

Therefore, when installing foil faced insulation always fit the foil side where the temperature difference is greatest. So, any time you use a single side foil insulation, the foil needs to be facing toward the living space. So in a loft the foil faces downward.

Does it matter what side of insulation faces out?

When installing faced insulation, the facing should always point toward the interior, heated, or air-conditioned space. For example: On exterior walls, the facing should touch the drywall. In attics, the facing should point down toward the ceiling below.

Reflective Bubble Foil Insulation/Does It Work???

Does foil insulation keep heat out?

The reflective surface of the foil layer creates a barrier that prevents heat from passing through the insulation and into the living space. The effectiveness of foil insulation can be increased by leaving an air gap between the foil layer and the surface it's installed on.

Should there be an air gap between insulation and roof?

Should you leave a gap between the insulation and the roof? Yes, you should leave an air gap between the insulation and the roof to allow proper ventilation and prevent moisture buildup.

How should reflective insulation be installed?

Roll out the product across the top of the trusses, pull tight and staple at approximately 4” intervals. Run subsequent courses of the product with the 3/4” staple tabs overlapping at the seams. Tape the seams with a Reflectix® Foil Tape (goal is an air-tight, snug seam seal). Install purlins over the insulation.

Should silver side of insulation board go in or out?

If there is no dead air space, it doesn't matter which way the metallic side is facing. Placing the metallic facer towards an open-air space may allow the material to act as a radiant barrier.

Is foilboard insulation any good?

Unlike traditional bulk insulation and insulated batts, Foilboard® GREEN's slimline profile makes for an ideal thermal break and vapour barrier, and with its superior thermal performance, it ensures a continuous “eskie” effect to the building year round.

What does "keep the shiny side up" mean?

Shiny side up. Your vehicle hasn't flipped over after a rollover or accident. “Keep the shiny side up” means to have a safe trip.

Which side of foil reflects heat on Reddit?

Fun fact. Both sides are just as reflective as each other. The difference is that one reflects light and heat in the same direction like a mirror, while the other reflects it in random directions (technical term is random scatter). So no, no difference.

Does foilboard need an air gap?

Does Foilboard need an air gap? In most applications, foil insulation requires an air gap of at least 25mm in order to insulate effectively for radiant heat. Installed without an air gap, and the effective R value of the boards will be close to zero.

Can you board over foil insulation?

If you plan to add an extra layer of insulation, you can install insulated plasterboards over the foil insulation.

Should you leave an air gap between the insulation and the boards?

It's important to leave a ventilated air gap between the insulation and the boards to prevent condensation on the underside of the boards.

What is the disadvantage of foil insulation?

One of the disadvantages of foil insulation is that it is not as effective against convection and conduction as it is against radiant heat.

Is it illegal to put aluminum foil on windows?

Emergency management agencies specifically recommend using aluminum foil-covered cardboard that goes between windows and drapes.

What is the minimum air gap between roof and insulation?

An air gap will need to be 50mm wide, and the best way to ensure this is to attach timber battens of a 50mm width within your roof, which you can then place the insulation boards against. Use tantalised roofing battens of 50mm. These should be attached to the roof joists using a screwdriver or a nail gun.

Does pink insulation have asbestos?

What is the pink fluffy stuff on the walls? The pink fluffy material is usually fiberglass insulation, commonly used for its safety and efficiency. It does not contain asbestos.

What is the purpose of kraft paper on insulation?

What is the difference between unfaced and Kraft-faced insulation and how is it installed? Unfaced means the insulation lacks a vapor retarder (paper or plastic facing). Kraft-faced insulation includes a paper vapor retarder, which helps prevent mold and mildew.

Where should you not put insulation?

Never place insulation close to water heaters, oil burners or anything hot. The backing is especially flammable and will be a major fire hazard for your home.

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