Which is better for exterior walls?

The Johns Manville roll, because its kraft facing is a vapor retarder. The Knauf roll is unfaced, so you would need to add a separate vapor barrier on exterior walls.

Do they insulate the same?

Yes. Both are R-19 fiberglass at about 6.25 to 6.5 in. thick, so the thermal difference is negligible. The gap is in facing, width and coverage.

How many rolls do I need?

Divide your square footage by 48.96 for Knauf or 75.07 for Johns Manville. A 500 sq ft wall takes about 11 Knauf rolls or 7 Johns Manville rolls.

Is the Knauf roll worth it over the Johns Manville?

It is worth it if you want GREENGUARD Gold, ECOSE binder and unfaced insulation for interior walls or between floors. For exterior walls, the Johns Manville facing saves a step.

Which is better for sound control?

Both reduce sound. The Knauf roll is marketed for acoustic use in interior walls and between floors, and its unfaced form lets you add resilient channels and a separate barrier more easily.

Can I use the kraft-faced roll in a ceiling?

Yes. Johns Manville lists ceilings and floors as suitable surfaces. Keep the kraft facing toward the heated side and seal the seams.

Knauf R-19 Unfaced Fiberglass Insulation Roll vs Johns Manville R-19 Kraft Faced Insulation Roll

Buy the Johns Manville roll for walls and ceilings where you want a built-in vapor retarder and fewer seams: its 23 in. width covers 75.07 sq ft per roll versus 48.96 sq ft for the 15 in. Knauf. Buy the Knauf roll for interior walls and between floors where you want unfaced, formaldehyde-free, GREENGUARD Gold insulation and will add your own vapor barrier. Both are R-19 and 6.25 to 6.5 in. thick, so thermal performance is the same; the choice comes down to facing, width and coverage.

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