Which is better for 2x4 walls?

The Owens Corning R-13. At 3.5 in. it fits a 2x4 cavity and its facing acts as the vapor retarder. The Knauf Ecobatt is 8 in. thick and will not fit.

Which gives more insulation per inch?

The Knauf. It reaches R-21 in 8 in., about 2.6 R per inch, while the Owens Corning is R-13 in 3.5 in., about 3.7 R per inch. The Owens Corning is more efficient per inch but tops out lower.

Do I need a vapor barrier with the Knauf?

Yes, in wall applications. The Ecobatt is unfaced, so add a separate vapor retarder. Knauf does sell kraft, foil and FSK-25 faced versions of this line.

Which covers more area per pack?

The Owens Corning, at 148.54 sq ft versus 67.81 sq ft for the Knauf. You need roughly two Knauf packs to match one Owens Corning pack.

Is the Knauf worth it for an attic?

Yes, if your joists are deep enough for 8 in. batts. R-21 beats R-13 for attic thermal performance, and the unfaced form is fine where no vapor retarder is required.

Both are fiberglass batts and last decades when kept dry. The Knauf adds documented mold resistance (ASTM C1338) and low vapor sorption, which helps in damp spaces.

Owens Corning R-13 Faced Insulation Batt vs Knauf Ecobatt R-21 Fiberglass Insulation

For a standard 2x4 wall, buy the Owens Corning R-13. It is 3.5 in. thick, faced with a vapor retarder, and covers 148.54 sq ft per pack, which fits 2x4 framing directly. The Knauf Ecobatt is R-21 and unfaced, so it suits 2x6 walls, attics and manufactured housing where more depth is available. Both are fiberglass batts with strong ratings; the Knauf scores slightly higher (4.8 from 53 ratings vs 4.7 from 134).

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