Radiant barriers reflect radiant heat.
Fiberglass attic insulation vs reflective.
Reflective insulation is significantly thinner than fiberglass insulation.
Radiant barriers and reflective systems.
What is the right insulation for an attic.
The reflectix site provides a great range of information about this and about how it differs from other types of 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.
Air migrates from warmer spaces toward colder spaces and insulation is designed to help prevent or at least slow that migration.
Both types of heat are trying to enter your home on a hot summer day.
Remember traditional attic insulation has r value that works to slow conductive heat.
The key to using reflectix properly is that you should take a little time to understand how reflective insulation works in the first place.