Traditional Felt vs. Synthetic Underlayment

Friday, June 8th, 2018 by Sydney Stewart

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What is Underlayment?

Strictly speaking, underlayment is another layer between the decking of your roof and your new asphalt shingles. It is a secondary barrier that is critical to helping preserve the overall roofing system that was just installed on your home. This water-resistant barrier is installed directly onto the plywood of your roof’s deck. It is applied underneath all other roofing materials for an added layer of protection from severe weather.

There are two main types of underlayment commonly used on residential homes: traditional asphalt-saturated felt and non-bitumen synthetic underlayment.

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Interwarp's RhinoRoof synthetic underlayment installed in Loves Park, IL

Roof Replacement in Janesville, WI - Before Photo Roof Replacement in Janesville, WI - After Photo

Asphalt-Saturated Felt

Traditional roofing felt is a felt paper that is soaked in asphalt. It is combines with other water-resistant compounds that produce a membrane. These compounds include varying blends of cellulose, polyester, and bitumen. This type of roofing material was the go-to for many years, up until about 15 years ago. It is still used in residential jobs due to the lower price point than the newer materials.

Non-Bitumen Synthetic Underlayment

The newest water-resistant underlayment is referred to as “Synthetic Underlayment”. This material is saturated in asphalt and then spun with either polyethylene or polypropylene. The addition of fiberglass gives these products superior resistance to tearing and increased stability.


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FeltBuster Synthetic Underlayment installed in Antioch, IL

Why Synthetic Underlayment is the Better Choice

Though synthetic underlayment has a greater cost, it has much greater benefits to homeowners.

  • Safety

    • Synthetic materials provide slip-resistant surface for the people who are installing the roof. This allows the workers to move around the roof with ease when installing shingles or other roofing materials.

    • The synthetic materials are lightweight and easier to handle than traditional felt paper. This means less trips up and down the home on ladders to retrieve the product.

  • Strength

    • The synthetic material is much for resistant to tearing than the traditional felt. Since it is less likely to rip, there is a lower risk of potential water infiltration in the future.

    • Additionally, synthetic materials can withstand UV exposure much longer than felt paper, so if progress needed to halt on a roof before the shingles were laid, the material will not be damaged. For example, Interwrap’s RhinoRoof can be exposed to UV rays for up to 60 days without any potential damage.

  • Installation

    • Many synthetic underlayments are printed with the crew in mind. This means they are printed with overlap nail guides.

    • Synthetic materials are also printed longer and wider than the traditional felt, making the product go further on the roof. This means less trips and a quicker installation due to less cutting time.

  • Water

    • Synthetics are designed to repel water. Traditional felt is designed to absorb water. While these both help keep water out of the home, the synthetic material is getting the water off of the roof, versus keeping it there until it can dry out.

    • Since the synthetic material repels the water, it is not a breeding ground for mold, like traditional felt is. This means the homeowner does not have to worry about an infestation of mold underneath their shingles.

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CertainTeed RoofRunner synthetic underlayment installed in Rockford, IL 

My-Pros is proud to offer synthetic underlayment on all of our roofing jobs. Our crew is highly skilled in properly installing the synthetic material that will keep your home safe for many years to come.

My-Pros operates throughout the Northern Illinois and Southern Wisconsin region, in cities like Rockford, Machesney Park, Belvidere, and Beloit. Give us a call at 1-815-957-0770 or click here to schedule a free estimate!




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