Synthetic vs Felt Underlayment

01 / Understand the material

What changes between felt and synthetic?

Underlayment sits beneath the roof covering and provides a secondary layer of weather protection. Felt uses an asphalt-saturated mat; synthetic products use polymers. The material name is a starting point, rather than a complete specification.

Typical tradeoffs to confirm for the products quoted
Check	Felt	Synthetic
Handling	Often heavier for the area covered.	Often lighter, with more material per roll.
Tearing and moisture	Traditional felt can tear or wrinkle when wet.	Many products offer improved tear resistance and repel moisture.
Upfront price	Often the lower-priced material option.	Can have a higher upfront price; compare the full order.
Exposure	Check the exact instructions before leaving it uncovered.	A stated exposure period belongs to a particular product and its conditions.

Owens Corning’s felt and synthetic comparison describes these general tradeoffs and emphasizes that synthetic products differ in performance. Do not use a material family alone to predict service life, storm performance or warranty coverage.

02 / Compare the actual instructions

“Synthetic” does not specify how it attaches

Record the attachment method separately from the material. For example, Atlas Summit synthetic underlayment is a mechanically fastened product. Its published UV-exposure limit is a product-specific condition, not a promise that any synthetic sheet can serve as a finished roof.

Ask for the instructions that match the exact product, roof covering, substrate, slope and location. Confirm the permitted exposure, fastening, laps and required layers with the project team. A slip-resistant surface does not establish that a roof is safe to access.

GAF’s underlayment guidance explains that installation procedures differ between products and shows roof-deck protection and leak barriers as separate system components. Do not assume a field-underlayment order also covers a specified ice-and-water barrier.

03 / Make the quotations comparable

Keep these details beside each option

Exact product: Name, region, current technical document and the roof-system requirement it satisfies.
Installation basis: Attachment method, required layers, lap details and exposure conditions confirmed for the project.
Effective coverage: The area one roll covers under that installation method, with its unit. Check whether a stated roll area is gross material area or usable installed coverage.
Whole-order price: Whole rolls required and price per roll. List fasteners, accessories, delivery, tax and labor separately.

Use the same measured sloped roof area for both options. If you have only plan dimensions, the Roof Area Calculator converts verified geometry into sloped area. The pitch measurement guide helps when that input is missing.

04 / Check the whole-roll order

A cheaper area rate can still cost more to buy

Consider an illustrative 1,800 ft² sloped roof, one specified layer and a user-chosen 5% allowance. The ordering target is 1,800 + 90 = 1,890 ft². These are invented quotation values, unrelated to the manufacturers above. Assume both options have already been accepted for this example project.

Illustrative USD roll prices; effective coverage already reflects the intended method
Quantity or cost	Quote A	Quote B
Effective coverage per roll	180 ft²	900 ft²
Price per roll	$25	$110
Price per effective ft²	About $0.139	About $0.122
Exact rolls	1,890 ÷ 180 = 10.5	1,890 ÷ 900 = 2.1
Whole rolls to purchase	11	3
Roll material cost	$275	$330
Purchased effective coverage	1,980 ft²	2,700 ft²
Coverage beyond the ordering target	90 ft²	810 ft²

Quote B has the lower effective-area rate, but its larger package leaves more surplus and costs more for this order. That is a packaging result, not evidence that either material family is always cheaper or better.

The example recommends neither a layer count nor an allowance. It excludes labor, accessories, tax and delivery. Do not deduct laps twice if your effective coverage already accounts for them. Surplus coverage is purchased material beyond the target, not extra roof area or a guaranteed reusable offcut.

Next / Turn product data into an order

Compare rolls using your actual quotations

Once suitability and effective coverage are confirmed, enter each option in the underlayment calculator. It keeps roof area, layers, allowance, whole rolls, surplus and optional roll cost separate.

Calculate underlayment rolls

Keep the rest of the roof estimate separate

The Roof Shingle Calculator estimates field-shingle bundles as a separate purchase. Underlayment roll quantities do not establish the covering quantity, accessory schedule or complete installed price.

This guide compares product information and purchasing arithmetic. It does not approve an assembly, prescribe installation or local code requirements, plan roof access, or select a leak-barrier system. Resolve those decisions through the applicable project documents, current manufacturer instructions and qualified project team.

Manufacturer pages checked October 16, 2026. Document review only; no field testing, product endorsement or universal service-life claim.