Faced vs Unfaced Insulation: When to Use Each

Faced or unfaced — it's a two-word question that causes more moisture damage in homes than almost any other insulation decision. The kraft paper facing on a batt isn't decoration. It's a vapor retarder that controls moisture movement through walls and ceilings. Put it on the wrong side, double it up, or use it where it doesn't belong, and you create the conditions for mold, rot, and structural damage inside your wall cavity. The rules are straightforward once you understand the logic.

Quick Answer: Use faced (kraft-paper) insulation for new exterior walls in cold climates (zones 4 Marine through 8) with the facing toward the warm interior side. Use unfaced when adding insulation over existing, in hot-humid climates (zones 1–3), for interior walls, or when another vapor retarder is already present. The cardinal rule: never trap a vapor retarder between two insulation layers — it creates a moisture sandwich that can't dry in either direction.

Table of Contents

• What Is Faced Insulation?
• Vapor Retarder Classes
• When to Use Faced Insulation
• When to Use Unfaced Insulation
• Climate Zone Guide for Vapor Strategy
• The Moisture Sandwich Problem
• Smart Vapor Retarders
• Common Mistakes
• Key Takeaways
• FAQ

---

What Is Faced Insulation?

Faced insulation is a standard fiberglass or mineral wool batt with kraft paper (or occasionally foil) laminated to one side. That paper layer is a Class II vapor retarder with a permeance of approximately 1 perm — it slows moisture vapor from passing through the insulation from the warm, humid side of the assembly to the cold side.

Three things the facing is NOT:

• Not an air barrier. Kraft paper has staple holes, seams, and isn't sealed at edges. It does almost nothing for air leakage. For air sealing, you need caulk, foam, or tape at every penetration and gap — the insulation facing doesn't substitute. Read more at air sealing vs. insulation.
• Not a moisture barrier. At ~1 perm, kraft facing slows moisture movement — it doesn't stop it. Bulk water (leaks, flooding) passes right through.
• Not optional in all climates. The 2021 IRC (Section R702.7) requires a vapor retarder on the warm side of exterior wall insulation in climate zones 5 and above. Kraft facing satisfies this requirement. The DOE's insulation guidance provides additional context on vapor retarder placement by climate.

The facing is typically installed by stapling the paper flanges to the faces or sides of studs during new construction. In ceiling applications, the facing goes against the ceiling drywall (toward the heated space below).

---

Vapor Retarder Classes

Understanding the three classes of vapor retarders puts the faced vs unfaced decision in context.

The 2021 IRC Section R702.7 requires Class I or II vapor retarders on the warm side of exterior walls in zones 5–8, and Marine Zone 4. Zones 1–4 (except Marine 4) are exempt or allow Class III. Building Science Corporation's vapor retarder guidance provides the technical background.

The key principle: moisture vapor moves from warm/humid air toward cold/dry air. In winter in a cold climate, that means from inside to outside. The vapor retarder goes on the warm side to slow this movement before moisture reaches a cold surface and condenses. In summer in a hot-humid climate, the vapor drive reverses — moisture pushes inward from hot, humid outdoor air. That's why you don't want a vapor retarder on the interior side in hot climates — it would trap inbound moisture.

---

When to Use Faced Insulation

1. New exterior wall construction in cold climates (zones 4 Marine through 8). Kraft facing toward the interior (warm side). This is the most common application and the scenario the product was designed for. The facing provides the Class II vapor retarder required by code in zones 5+.

2. Cathedral ceilings. Faced batts between rafters with the kraft paper toward the interior (heated space). This slows moisture migration into the roof assembly. Note: in vented cathedral ceiling assemblies, you still need a ventilation channel between the insulation and the roof deck.

3. Floors over unconditioned spaces. When insulating a floor above an unheated crawl space or garage, faced batts go between the joists with the facing UP — toward the heated room above. The warm side is the living space; the cold side is the unheated space below.

4. First layer in new attic construction. If you're installing batts on an attic floor in new construction (before drywall is installed from below), faced batts go with kraft paper DOWN, toward the heated space below. Once drywall is up, this creates the vapor retarder on the warm side of the ceiling assembly.

Pro Tip: The facing always goes toward the warm side of the assembly. In heating climates, that's the interior. Mentally picture where the warm, moist air is — the facing goes on that side to slow moisture from moving toward the cold side and condensing. If you can't figure out which side is warm, you probably don't need a vapor retarder (you're likely in a mixed or warm climate where Class III vapor retarder, i.e., latex paint on drywall, is sufficient).

---

When to Use Unfaced Insulation

1. Adding insulation over existing insulation. This is the most critical unfaced application. If you're blowing cellulose or fiberglass on top of existing attic insulation, or adding a second layer of batts, the new insulation must be unfaced. A vapor retarder sandwiched between insulation layers traps moisture with no drying path — the "moisture sandwich" problem we cover below.

2. Hot-humid climates (zones 1–3). In cooling-dominated climates, moisture drives inward — from hot, humid outdoor air through the wall toward the air-conditioned interior. An interior vapor retarder (kraft facing) would trap that inbound moisture inside the wall. Latex paint on interior drywall (Class III, ~5 perms) provides sufficient vapor management in these climates. Use unfaced batts.

3. Interior partition walls. Walls between two conditioned rooms have no temperature differential and no meaningful moisture drive. Vapor retarders are unnecessary. Use unfaced batts — typically for soundproofing purposes only.

4. When another vapor retarder already exists. If the assembly already has polyethylene sheet (common in zone 7–8 construction), vapor-retarder paint, or foil-faced sheathing, adding kraft-faced batts creates a double vapor retarder. Use unfaced.

5. Exterior continuous insulation (ci) assemblies. When rigid foam board is applied to the exterior of the wall sheathing, the foam itself may serve as the vapor retarder (foil-faced polyiso is <0.05 perms; XPS at 2" is ~0.5 perms). Adding kraft facing on the cavity batts creates a potential moisture trap. Many building scientists recommend unfaced cavity insulation when exterior ci is present — check wall insulation for assembly-specific guidance.

---

Climate Zone Guide for Vapor Strategy

This table tells you what vapor management strategy fits your climate. Use our climate zone map to find your zone.

The 2021 IRC Section R702.7 codifies this: zones 5 and above (plus Marine 4) require a Class I or II vapor retarder on the warm side of exterior wall framing. Kraft-faced batts satisfy this requirement. Zones 1–4 (except Marine) are exempt from interior vapor retarder requirements.

---

The Moisture Sandwich Problem

This is the #1 moisture failure mode we see related to faced insulation — and it's entirely preventable.

What happens: A homeowner in zone 5 has R-19 kraft-faced batts in the attic floor (facing down, toward the heated ceiling — correct). They want to add R-30 to reach R-49. They buy kraft-faced R-30 batts and lay them on top, creating this assembly:

[Attic air — cold in winter]
R-30 batt (kraft facing on bottom)  ← PROBLEM: second vapor retarder
R-19 batt (kraft facing on bottom)  ← original, correctly placed
[Drywall ceiling — warm side]

Now there are two kraft-facing layers sandwiching the R-19 batt. In winter, moisture vapor from the heated space below moves upward through the ceiling drywall, through the first (correct) vapor retarder, and hits the second vapor retarder on the bottom of the R-30 batt. It condenses on that cold kraft paper surface. The trapped moisture has nowhere to go — it can't dry upward (second facing blocks it) or downward (first facing blocks it). Result: wet insulation, mold growth, and potential ceiling damage.

The fix: Always use unfaced insulation when adding layers. If you're adding blown-in over existing faced batts, slash or perforate the existing kraft facing so moisture can pass through freely. If you're adding unfaced batts on top, simply lay them perpendicular to the existing batts (no stapling needed — gravity holds them).

Pro Tip: If you bought faced batts by mistake for an addition-over-existing job, you can still use them — just install them with the facing UP (toward the cold attic side). This puts the vapor retarder on the wrong side, but in an attic application the kraft paper won't cause problems because the attic side is ventilated and moisture can escape. It's not ideal, but it's vastly better than creating a moisture sandwich with the facing between layers.

---

Smart Vapor Retarders

In mixed climates (zones 3–5) where vapor drive reverses seasonally — outward in winter, inward in summer — both faced and unfaced batts are imperfect solutions. Smart vapor retarders solve this problem.

CertainTeed MemBrain: A nylon membrane installed like poly sheet but with variable permeance. In winter (low humidity), it tightens to approximately 1 perm — acting as a Class II vapor retarder that slows outward moisture drive. In summer (high humidity), it opens to 20+ perms — allowing inward moisture to pass through and dry toward the interior. This prevents both winter condensation and summer moisture trapping.

Pro Clima Intello Plus: Similar variable-permeance concept. Widely used in high-performance building projects.

When smart retarders make sense:

• Mixed climates (zones 3–5) where traditional faced batts risk trapping summer moisture
• Wall assemblies where exterior continuous insulation changes the vapor dynamics
• High-performance homes targeting airtightness below 2.0 ACH50 (where traditional vapor retarder rules may not apply)
• Old houses with complex wall assemblies where seasonal moisture flow is unpredictable

Smart retarders add $0.15–$0.30/sq ft in material — negligible on a wall project. They're increasingly specified by building scientists and energy consultants for any project in zones 4–5 where the vapor drive direction isn't clear-cut.

---

Common Mistakes

1. Facing toward the wrong side. In heating climates (zones 5+), the facing must go toward the warm interior. We've seen installations where kraft facing is placed toward the cold exterior — this traps interior moisture against the cold sheathing, causing condensation and rot. Remember: facing toward the warm side, always.

2. Doubling up vapor retarders. Two vapor retarders with insulation between them create a moisture trap. Never place kraft-faced batts over existing faced insulation. Never install poly sheet on the interior if kraft-faced batts are already in the walls. One vapor retarder per assembly — on the warm side.

3. Using faced batts when adding to existing insulation. The addition layer must be unfaced — whether you're adding batts on top of existing batts in an attic, or blowing cellulose over existing faced insulation. If the existing insulation has kraft facing, slash it before adding blown-in on top.

4. Using poly sheet in warm or mixed climates. Polyethylene sheet (Class I, <0.1 perms) is appropriate only in extreme cold climates (zones 7–8). In zones 1–5, poly on the interior traps summer moisture inside the wall. Building Science Corporation has documented widespread moisture failures from poly in mixed climates. Use kraft facing (Class II) or smart retarders instead.

---

Key Takeaways

• Faced insulation has kraft paper (~1 perm, Class II vapor retarder) on one side. It slows moisture migration from warm/humid air toward cold surfaces.
• Use faced batts for new exterior walls in cold climates (zones 4 Marine through 8) with facing toward the warm interior side. Also for cathedral ceilings and floors over unconditioned spaces.
• Use unfaced batts when adding insulation over existing, in hot-humid climates (zones 1–3), for interior walls, and when another vapor retarder is already present.
• Never sandwich a vapor retarder between insulation layers. This traps moisture and causes mold and rot. Always use unfaced when adding to existing insulation.
• The 2021 IRC (Section R702.7) requires a Class I or II vapor retarder on the warm side in zones 5+ and Marine 4.
• Smart vapor retarders (MemBrain, Intello Plus) adapt their permeance to seasonal conditions — ideal for mixed climates (zones 3–5).
• When in doubt about faced vs unfaced, check your climate zone and default to unfaced with latex paint as the Class III retarder. This is safe in zones 1–4 and won't cause moisture problems.

---

FAQ

Which do I need — faced or unfaced insulation?

It depends on your climate zone and whether existing insulation or another vapor retarder is already in place. In cold climates (zones 5–8), use faced batts on new exterior walls with the kraft paper toward the interior. In hot-humid climates (zones 1–3), use unfaced. In mixed climates (zones 3–4), either works — faced with paper toward interior, or unfaced with latex paint as the Class III retarder. If you're adding to existing insulation, always use unfaced. The R-value chart and vapor barrier guide have more detail.

Does it matter which way the facing goes?

Absolutely — this is one of the most consequential installation details for long-term wall performance. The facing always goes toward the warm side of the assembly. In heating climates (most of the US), that's the interior. The kraft paper slows moisture from the warm, humid indoor air before it reaches the cold outer wall surface and condenses. Reversing the facing traps moisture against the cold sheathing — causing condensation, mold, and potential structural damage.

Can I use faced batts in an attic?

For a new attic (first installation, before drywall is up): yes, with facing toward the heated space below (facing DOWN in a ceiling application). For adding insulation over existing: no — use unfaced batts or blown-in insulation. If you're blowing cellulose or fiberglass over old faced batts, slash the existing kraft facing so moisture can move through freely. See our attic insulation guide for the complete approach.

What if I'm adding insulation over existing?

Always use unfaced insulation for the additional layer. If the existing batts have kraft facing, you have two options: (1) slash the old facing to let moisture pass through, then blow new insulation on top, or (2) lay unfaced batts perpendicular over the existing batts. Never add a second layer of faced insulation — the trapped vapor retarder between layers creates a moisture sandwich. R-values are additive regardless of facing — existing R-19 plus unfaced R-30 on top gives you R-49.

What is a smart vapor retarder?

A smart vapor retarder is a membrane with variable permeance that adapts to humidity levels. In dry winter conditions (~30% RH), it tightens to approximately 1 perm — acting as a Class II retarder that slows outward moisture movement. In humid summer conditions (~60%+ RH), it opens to 20+ perms — allowing inward moisture to pass through and dry toward the interior. Brands include CertainTeed MemBrain and Pro Clima Intello Plus. They're ideal for mixed climates (zones 3–5) where traditional faced batts or poly sheet create seasonal moisture risks. They add $0.15–$0.30/sq ft — a negligible cost for the moisture management benefit.