The key to using reflectix properly is that you should take a little time to understand how reflective insulation works in the first place.
Fiberglass attic insulation vs reflective.
Reflective insulation is significantly thinner than fiberglass insulation.
If your attic has a lot of nooks and crannies your best bet may be to use loose fill insulation made of fiberglass or cellulose.
Which is better will depend on the topography of the specific roof you re insulating.
Both types of heat are trying to enter your home on a hot summer day.
The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the attic insulation.
Radiant barriers and reflective systems.
The radiant barrier resulted in roughly 4 times more savings than the added insulation.
Next i compared adding an additional r 19 to my existing r 19 level of attic insulation vs installing radiant barrier and the results actually surprised me a little.
Remember traditional attic insulation has r value that works to slow conductive heat.
Air migrates from warmer spaces toward colder spaces and insulation is designed to help prevent or at least slow that migration.