Synthetic vs. Felt: Which Roofing Underlayment is Right for You?

A roofer installing underlayment for a roof.

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    Why Roofing Underlayment Is Needed

    Roofing underlayment is material underneath the roof’s shingles used to protect a home or business when heavy rain, snow, or wind occurs. Most areas around the United States require homes and businesses to have synthetic or felt underlayment. Roof underlayment does not only provide a home and business with extra protection that shingles can not do, but it is also a form of moisture protection as well. Shingles are good for protecting a roof against sun rays and they are the first line of defense for covering a roof. However, there are certain things that shingles cannot protect against and that is heavy rain, wind, and snow. Shingles age over time and can become brittle. Shingles can also be lifted off the roof by strong winds; this is why roof underlayment is needed.

    The Advantages And Disadvantages Of Using Felt Underlayment

    Felt underlayment is also known as felt paper or tar paper. This type of underlayment was the primary type used until about 15 years ago when synthetic underlayment was created. Felt underlayment is made of four different materials: cellulose, asphalt, polyester, and bitumen. Felt underlayment is still used in certain situations where there is a lot of rain. The reason being is that this type of underlayment is highly water-resistant. Because of this water resistance, the roofer that does a job on a home or business may recommend this type of underlayment over a synthetic underlayment. The advantage to using felt underlayment is that it can be found in different thicknesses and has different resistance levels. Felt underlayment provides a great seepage barrier, is not expensive, and can be easily installed.

    The main disadvantage to using felt underlayment is that it is extremely heavy. Felt underlayment also tends to crack and wrinkle when exposed to extreme cold. Felt underlayment can also have an adverse reaction to excessive heat as well. Severe heat causes felt underlayment to absorb more moisture and more moisture causes it to break apart.

    The Advantages And Disadvantages Of Using Synthetic Underlayment

    Synthetic underlayment is the most preferred roofing underlayment used today by professional roofers. Synthetic underlayment is made of asphalt and fiberglass. These two materials combined give synthetic underlayment the best resistance and stability of all the available roof underlayment. Some roofing professionals also combine synthetic underlayment with other waterproofing products. One of the main advantages of synthetic underlayment is that it does not add a lot of weight to the roof because it is such a light material. Mold and fungus do not grow on synthetic underlayment because it does not absorb moisture. Synthetic underlayment is also wind-resistant, so it does not tear easily. Lastly, synthetic underlayment does not wear down as quickly as felt underlayment because it can withstand cold weather better.

    There are disadvantages associated with synthetic underlayment. This type of underlayment is costly and can be very difficult to install. It also requires more tools to be used than installing felt underlayment.


    When it comes to choosing the right type of underlayment, there are several factors to consider. The main factors to keep in mind and weigh are costs vs protection. If you can afford synthetic underlayment, it’s the better choice, but if you’re looking to save money you may want to go with felt underlayment. Speaking with local roofing experts can help you decide what is right for you.

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