The Ultimate Guide to Siding Underlayments: Housewraps and Exterior Insulation

Choosing the right underlayment beneath your siding isn't just about what's available—it's about how well your home breathes, stays dry, and conserves energy. This guide breaks down the two main types of siding underlayments:

• Housewraps – breathable, water-resistant layers

• Exterior Insulations – rigid or reflective rolls or panels that improve thermal performance

Category 1: Housewraps (Weather-Resistive Barriers)

These materials are applied directly over wall sheathing to prevent water infiltration while allowing vapor to escape. Here they are ranked from highest to lowest performance.

Ranked by Performance

1. DELTA®-VENT SA

• Performance: Excellent

• Price: $$$$

• Type: Fully adhered, vapor-permeable WRB

• Highlights: Outstanding air sealing, no fastener holes, ideal for high-performance building envelopes

2. Tyvek® CommercialWrap / HomeWrap

• Performance: Very Good

• Price: $$$

• Type: Spun-bonded breathable membrane

• Highlights: Durable, water-resistant yet breathable, trusted brand

Tyvek housewrap installed under new siding - JP Construction Services

3. Typar® HouseWrap

• Performance: Good

• Price: $$

• Highlights: High tear resistance and UV durability, slightly less breathable than Tyvek

4. Barricade® Wrap Plus

• Performance: Fair

• Price: $$

• Highlights: Adequate water resistance, lower breathability and longevity

5. Generic Micro-Perforated Wraps

• Performance: Poor

• Price: $

• Highlights: Perforated plastic that allows bulk water intrusion; outdated option

Category 2: Exterior Insulation (≤ 1" Thick or Slightly Over)

Exterior insulation improves energy efficiency, reduces thermal bridging, and helps walls stay warm and dry. Below, these are ranked by total R-value (R-value is a measure of thermal efficiency. The greater the R-value, the greater the efficiency)

Ranked by Total R-Value (Highest to Lowest)

1. Foil-Faced Polyisocyanurate (Polyiso)

• Thickness: 1 inch

• R-Value: 6.5

• Price: $$$

• Pros: Highest R-value in thin foam boards, reflects radiant heat

• Cons: May lose performance in cold climates

2. Tyvek® ThermaWrap® R5.0

• Thickness: 1.5 inches

• R-Value: 5.0

• Price: $$$$

• Pros: Combines WRB and insulation in one, great for streamlining wall assemblies

• Cons: Thicker than others on this list; more costly

3. Low-E Reflective Insulation

• Thickness: ~1/4 inch

• R-Value: 4.16 (with required air gap)

• Price: $$

• Pros: Thin and easy to install; blocks radiant heat

• Cons: Requires air gap to reach rated R-value; not bulk insulation

Low-E insulation installed under new siding - JP Construction Services

4. Expanded Polystyrene (EPS)

• Thickness: 1 inch

• R-Value: 3.85 – 4.2

• Price: $$

• Pros: Affordable, easy to work with

• Cons: Can absorb moisture if not faced

5. 5/8” FanFold EPS

• R-Value: 2.7

• Price: $$

• Pros: Helps level walls and adds light insulation

• Cons: Limited thermal value

6. 1/2” FanFold EPS

• R-Value: 2.0

• Price: $

7. 3/8” FanFold EPS

• R-Value: 1.5

• Price: $

3/8" foam insulation installed behind new siding - JP Construction Services

Final Thoughts

• For maximum thermal performance in minimal thickness, Foil-Faced Polyiso leads the way.

• Tyvek® ThermaWrap® R5.0 is ideal when you want both a WRB and insulation in one step.

• Fanfold and Low-E are great for low-profile, budget-conscious upgrades—just don't expect high insulation values.

• Pairing a high-performance housewrap with exterior insulation is the best strategy for energy-efficient siding installations.

In the market for new siding? Make sure to choose a contractor that can explain all your different siding underlayment options, so you get the product that makes the most sense for your home and for your budget. If you live within our service area, call us today at (877) 846-9566, or fill out the form below. Or, if your siding has sustained hail or wind damage, schedule your free inspection online.