Which gives better insulation, R-49 or R-38?

R-49 insulates better. It has about 29% more thermal resistance than R-38, which matters most in cold climates and on exterior walls and ceilings.

Do I need a vapor barrier with the R-38?

In most cold climates, yes. The unfaced R-38 has no facing, so you add a separate vapor retarder on the warm side. The R-49 kraft facing serves that role.

Can I use the R-49 batts in interior walls?

You can, but the kraft facing can trap moisture in interior partitions. Unfaced R-38 is the safer pick for interior walls and sound control.

Which is easier to install?

The unfaced R-38 is simpler because there is no facing to orient. The R-49 needs the kraft side facing the warm side of the wall.

Is one worth the extra cost?

For exterior walls and attic ceilings in a cold climate, the R-49 usually is, because it meets higher R-value targets in one layer. For interior walls, the R-38 is the better value.

Are both safe for indoor air?

Yes. Both are GREENGUARD certified, so they meet low-emission standards for indoor air quality.

Knauf Ecobatt R-49 Insulation Batts vs Knauf R-38 Fiberglass Insulation Batt

Buy the R-49 kraft-faced batts for exterior walls, ceilings and any cavity where you want a vapor retarder and the highest R-value per inch of cavity. Buy the R-38 unfaced batts for interior partitions, sound control, or where a separate vapor barrier already exists or is not wanted. Prices were not provided for either product, so check the current price per square foot at each store before deciding.

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