An attic baffle is simply an item to regulate the flow of air aka required roof venting and impede it the insulation from interfering with each other.
Foam attic air baffles.
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Baffles provide a channel for air to flow through certain parts of the attic.
If you re insulating a ceiling and need to maintain an air sealed vent space from the soffit all the way to the ridge you could use plastic vent baffles stapled into place between the rafters and try to air seal them but there s a better way.
They also keep insulation from falling into and clogging up the eaves.
They can reduce roof deck temperature minimize ice dam issues and can help control attic moisture.
Attic baffles how they work.
The picture below courtesy of the epa indoor airplus program which we provide builder verification services for helps show how the system works.
From left to right air flows through the soffit vents up over the baffles allowing for the required roof venting.