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Synthetic vs. Felt Underlayment: Which One Is Right?
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Synthetic vs. Felt Underlayment: Which One Is Right?
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Synthetic vs. Felt Underlayment: Which One Is Right?

Posted on May 13, 2024

Estimated Reading Time : 5 Min.

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Synthetic vs. Felt Underlayment

Every part counts when it comes to roofing. Every layer, from the flashing to the shingles, is essential for protecting your home from the weather. Underlayment is frequently regarded as one of the most overlooked parts of a roofing system among these components. 

There are many types of underlayment available, but two of the most common are synthetic and felt. This material helps to keep your home safe and dry by adding a layer of protection between the roofing material and the roof deck. In this blog post, we’ll discuss synthetic vs. felt underlayment to help you select the best option for your roofing needs.

Understanding Roof Underlayment

Found directly on the roof deck, the roofing underlayment is crucial for protecting homes from the weather. It serves as a barrier to keep out water before additional roofing components are installed, whether it is waterproof or not. Its primary function is to strengthen the roof deck and prevent leaks, mold, and rot caused by snow and rain. It can also increase fire safety and protect against severe weather and ice damage. Underlayment makes the roof look better by offering a smooth surface for installing shingles.

Now that you know what roof underlayment is, let’s delve in and understand the different types: synthetic and felt underlayment. 

What Is Felt Underlayment?

Felt underlayment

Felt underlayment is a strong roofing layer that, when installed properly, can last up to 30 years. It is made of organic materials such as paper or fiberglass mats saturated with asphalt. The #30 version, which is appropriate for roofs with steep pitches and is thicker than the #15 options, is especially durable during installation. 

This underlayment is less expensive than synthetic options, but it can tear easily during installation or in severe weather, and it can wrinkle from absorbing moisture. Additionally, its weight makes handling and installation more difficult, which could increase overall installation costs.


  • Cost-Effective: More affordable than other underlayment options.
  • Permeable: Allows for breathability.
  • Easy Installation: Requires only standard tools.


  • Prone to Ripping: Susceptible to damage if not handled with care.
  • Moisture Issues: May absorb water.
  • Weight Challenges: Heaviness makes it more difficult to install.

What Is Synthetic Underlayment?

Synthetic underlayment

Made of materials like polymers or polypropylene, synthetic underlayment serves as an additional barrier on top of the roof deck, blocking moisture and providing protection against wind-driven rain, ice dams, and possible damage to the roof. Synthetic underlayment has higher durability, tear resistance, and UV resilience than conventional asphalt-saturated felt. 

Although it’s not 100% waterproof, it provides temporary weather protection while construction is underway and creates a smooth surface for the final roofing material. It is easier to install and lighter than felt underlayment and lasts up to 25 to 50 years. Moreover, it provides benefits like increased resistance to mold and mildew, the ability to be left outside for longer periods of time, and increased security for roofers during installation because of its non-slip surface.


  • Durable: Long-lasting protection.
  • Lightweight: Easy to handle.
  • Waterproof: Prevents moisture infiltration.
  • Versatile: Works with various materials.
  • UV Resistant: Lasts under sunlight.


  • Costly: Higher upfront cost.
  • Puncture Risk: Prone to damage from debris or excessive foot traffic.
  • Moisture Trapping: Can cause mold if not properly ventilated.

Detailed Comparison: Synthetic Underlayment vs. Felt

1. Durability and Resistance

Synthetic underlayment is made of durable polymers and provides excellent durability and resistance to tearing in inclement weather. Because of its sturdy construction, roofs exposed to harsh weather can be reliably protected, providing contractors and homeowners with peace of mind. While offering some protection, felt underlayment is not as durable and can break down more quickly, particularly in regions that experience harsh weather.

2. Lifespan

With an average 25–30 year lifespan, synthetic underlayment outlasts felt alternatives, requiring fewer replacements over time and resulting in lower maintenance costs. Because felt underlayment only lasts 12 to 20 years, it needs to be replaced more frequently, which could result in higher long-term costs. When weighing total costs and maintenance requirements, homeowners who choose felt underlayment should take its shorter lifespan into account.

3. Weight

With a weight of 2 to 4 pounds per roofing square, or 100-square feet, synthetic underlayment is lightweight and easy to handle and install, which can reduce labor costs. On the other hand, felt underlayment poses difficulties during installation due to its heavier weight of approximately 15 pounds per square, which may mean additional labor and time.

4. Cost

While felt underlayment is less expensive initially, its shorter lifespan and higher maintenance requirements can lead to higher long-term costs. In contrast, synthetic underlayment, with its longer lifespan and durability, offers cost savings over time. 

5. Installation

The lightweight and tear-resistant characteristics of synthetic underlayment make it easier to install, improving efficiency and safety, whereas felt underlayment needs to be handled carefully to prevent problems like wrinkling or uneven surfaces, necessitating accuracy and close attention to detail during installation.

6. Appearance

Synthetic underlayment offers a smoother appearance for the finished roof, contributing to enhanced curb appeal and property value. Conversely, felt underlayment may be prone to wrinkling during installation, potentially detracting from the overall aesthetics of the roof.

7. Exposure Tolerance

Synthetic underlayment boasts impressive tolerance to UV rays and light rain, capable of withstanding prolonged exposure to the elements for extended periods. Felt underlayment, with a shorter exposure tolerance, may be more vulnerable to damage from moisture and UV rays, necessitating timely roof covering to prevent potential issues.

Factors to Consider When Choosing Between Roofing Felt vs. Synthetic Underlayment

1. Climate and Weather Conditions: 

Account for extreme temperatures or heavy rainfall in your area. Synthetic underlayment may excel due to its superior moisture resistance and wider temperature tolerance.

2. Roof Slope and Complexity: 

Evaluate the complexity of your roof structure. Synthetic underlayment might be preferable for intricate designs, offering enhanced durability and resistance against tears and punctures.

3. Budget: 

Compare the short-term and long-term costs. Even though synthetic underlayment might cost more upfront, over time its longer lifespan makes it more affordable.

4. Long-Term vs. Short-Term Costs: 

Consider the project’s budget and time constraints when making your decision. Synthetic options are appropriate for long-term investments, but felt underlayment can work well for short-term or cost-conscious projects.

5. Professional Roofer Recommendations: 

Seek advice from experienced roofers to learn industry insights and ensure the most suitable choice for your specific needs.

6. Roof Age and Condition: 

Assess whether your project involves a new roof installation or re-roofing. Synthetic underlayment offers added protection for new roofs, whereas felt may be adequate for re-roofing if the existing deck is sound.

7. Ease of Installation: 

Think of the level of expertise required for installation. Synthetic underlayment demands precision but may be worth the effort, while felt may be suitable for DIY or novice roofers.

8. Ventilation and Breathability: 

Factor in the attic or roof space’s ventilation capabilities. Felt underlayment’s breathability can help mitigate moisture buildup and potential mold or rot issues in poorly ventilated areas.

Synthetic Roof Underlayment vs. Felt: Which Underlayment Is Best?

The decision between felt and synthetic underlayment ultimately comes down to personal preferences and roofing needs. For some homeowners, the best option is synthetic underlayment if you are willing to spend more on a high-end product and value longevity and water resistance. 

On the other hand, felt underlayment is still an option for those who prioritize affordability and a track record of success. Making this decision depends on careful consideration of various factors, including cost, ease of installation, and longevity. A roofing expert can offer insightful information to guarantee that the choice suits your home’s requirements and will properly protect it over time.


The choice between felt and synthetic underlayment depends on your personal preferences. But with our expert services, you can find dependable roofing solutions that are customized to meet your needs. At All Around Roofing, Siding & Gutters, we have years of experience in the industry and can handle your project, whether you prefer felt underlayments for their affordability or synthetic underlayment for its greater durability. You can rely on our systematic strategy and dedication to excellence to protect your home. For quality roofing services, give us a call at (937) 902-2839.

Synthetic vs. Felt Underlayment
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