The best kind of rigid foam insulation is polyisocyanurate, also known as polyiso. It has the highest R-rating of any rigid foam insulation and comes with a reflective foil on both sides, allowing it to act as a radiant barrier as well.
Rigid foam board insulation is available in many materials, including polystyrene (R-3.8 to R-5.0), polyurethane (R-5.5 to R-6.5) and polyisocyanurate (R-5.6 to R-8.0). Since it has the highest R-value, rigid foam is typically reserved for foundations and basement walls.
Some of the best materials for thermal insulation are closed cell foams and urethane foams.
Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch.
R-Value In 2 Inches Of Spray Foam
Open-cell spray foam is vapor-permeable. The R-value ranges from R-3.5 to R-3.6 per inch. The filling of a 2×4 cavity yields about an R-13.
Thermablok® Aerogel is a revolutionary advancement in thermal technology offering the thinnest insulation available to prevent thermal and cold bridging. Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).
The optimal R-value for most homes is 30, but you can go as high as 38 if you live in a tropical climate. Anything higher than 38 indicates an over-insulated space.
Mineral Wool Insulation
In many ways, mineral wool is a superior insulation product. It has a higher R-value per inch compared to fiberglass, about a 22-37% higher R-value.
Latex foam is the highest-density foam, with an average rating of 5.6 pcf. This generally makes it a little too tough for a mattress, but it is an excellent option for a couch, bench, or outdoor patio furniture that you want to stand the test of time.
Polyiso is not very resistant to moisture absorption. It can absorb up to 3% of its weight in water when exposed to wet conditions. This can reduce its R-value and cause mold growth and rot.
I have just done an experiment on what makes the best insulator. I used 4 meterials (cups) polystyrene, paper, porcelain and metal. Polystyrene was the best insulator followed by paper, porcelainand then metal.
Closed cell foam is the best choice for robust insulating where space is an issue, as it can achieve 2x the R-Value of open cell inside a standard wall. Its rigid nature also adds to the structural integrity of the building and E84 fire rated versions are available.
If you need to increase insulation thickness or achieve a higher R-value, you can stack two sheets of Celotex insulation on top of each other. Celotex rigid boards are typically covered with aluminium foil on both sides.
Two-part closed cell spray foams have R values ranging from R-5 to R-6.1 per inch. Single-part Great Stuff™ sealants are used to fill smaller areas where air and moisture can flow.
Polyisocyanurate: Known as polyiso for short, polyisocyanurate foam has the highest R-value per inch (R-6.5 to R-6.8) of any rigid insulation. This type of rigid foam usually comes with a reflective foil facing on both sides, so it can also serve as a radiant barrier.
The thermal barrier of a home should consist of a continuous layer of insulation on all sides—including the lowest floor, the exterior walls, and the ceiling or roof. Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half.
R15 insulation offers slightly better thermal insulative properties than R13. Some of its formats are a fraction of an inch thicker than R13, making it more effective at helping with energy efficiency. However, the difference is minimal.
This microscopic difference in the two products creates a dramatic difference in performance. Closed cell spray foam has an R-value of R-7 per inch. In comparison, open cell spray foam has an R-value of R-3.8 per inch. Additionally, the materials have decidedly different densities.
Fiberglass: This insulation that looks like cotton candy is commonly seen in long strips — called batts or rolls — between wall studs and ceiling joists. It might be pink, white or yellow, and it also comes in a loose-fill form, often blown into attic spaces.
Mold and Mildew Growth
Having too much insulation in your attic can allow for the accumulation of moisture. This leads to mold and mildew growth, which can be extremely bad for your health.