What is the Best Roofing Underlayment? An Expert Breakdown of Felt vs. Synthetic

Most people think roofing starts and ends with shingles. They’re the visible part, the style choice, the piece everyone talks about. But what really protects your home is the layer you don’t see. Roofing underlayment sits between the shingles and the roof deck, acting as a critical barrier against rain, wind, and anything else the weather throws at you.

The type of underlayment you choose can make a big difference in how well your roof performs over time. In this guide, we’ll walk you through the two main types: felt and synthetic. You’ll learn the pros and cons of each, where they work best, and get expert insight from a trusted roofing professional who knows what holds up in the real world.

What Is Roofing Underlayment and Why Does It Matter?

Roofing underlayment is a water-resistant or waterproof sheet installed directly over the roof deck, just beneath the shingles. Although it’s not visible once the roof is finished, it serves a crucial purpose in protecting your home. You can think of it as a safety net; if the shingles are ever damaged or displaced, the underlayment helps prevent water and wind from penetrating the wooden structure underneath.

There are different types of underlayment, including traditional felt and more modern synthetic options. Regardless of the material, all underlayment is designed to provide that crucial extra layer of protection, especially in areas prone to heavy rain, strong winds, or snow. It also helps your roof meet local building codes and can improve fire resistance depending on the product used.

Key benefits of using roofing underlayment:

• Acts as a secondary barrier if shingles are damaged or dislodged
• Reduces the risk of leaks, mold growth, and wood rot
• Helps protect against wind-driven rain and moisture infiltration
• Adds another layer of insulation and energy efficiency
• Increases the overall durability and life expectancy of your roof

Using the right underlayment is not an upgrade. It’s a basic requirement for a long-lasting roof. Without it, your roofing system is more exposed to leaks, structural decay, and early failure. No matter how good your shingles are, a roof without proper underlayment is missing one of its most important layers.

Comparing Roofing Underlayment Types: Felt vs. Synthetic

When it comes to roofing underlayment, you’ve got two main players in the game: felt and synthetic. They might seem similar at first glance, but they perform very differently once they’re up on your roof. Understanding how each one works will help you make the right call for your home and budget.

Felt Underlayment (also known as tar paper)

Cons:

• Tears easily, especially during installation or windy weather
• Can absorb water, which defeats its own purpose
• Breaks down quickly with sun exposure

Best for: Homeowners on a tight budget, temporary roof protection, or quick repair jobs where long-term durability isn’t the priority.

Synthetic Underlayment

What it is:
Made from high-tech polymers like polypropylene or polyethylene, synthetic underlayment is designed to be strong, lightweight, and much more durable than felt. It’s quickly become the go-to choice for many modern roofing professionals.

Pros:

• Excellent water resistance
• High tear strength, even under foot traffic
• Holds up well against UV exposure
• Easy to handle, wrinkle-free, and lightweight

Cons:

• Higher upfront cost compared to felt
• Some types can be slippery unless textured or treated

Best for: Long-lasting roofing systems, homes in high-wind or high-moisture areas, and any build where durability and performance are a priority.

What the Expert Says: Real-World Advice from TSM Roofing

In a recent video from TSM Roofing, seasoned roofer Sheldon shares why his team consistently chooses synthetic underlayment for both residential and commercial projects. Based in Arizona, where roofs take a beating from intense heat and sun exposure, Sheldon has seen firsthand how different materials hold up over time.

Key insights from Sheldon’s experience:

• Predictable performance: Synthetic underlayment delivers consistent results across all types of installs, no matter the size or scope of the job.
• Built for harsh weather: In Arizona’s extreme heat, felt tends to break down quickly. Synthetic stays intact, even under prolonged UV exposure.
• Better moisture protection: Unlike felt, which can absorb water and degrade before shingles are even installed, synthetic keeps the roof deck dry and protected during the build.

“We’ve installed both over the years, and synthetic just gives us peace of mind that felt never did. It’s lighter, tougher, and doesn’t break down as fast.”
— Sheldon, TSM Roofing

Whether you’re roofing a starter home or a large commercial building, real-world results point to synthetic as the safer, smarter long-term investment.

Felt or Synthetic: Which Roofing Underlayment Is Right for You?

Still deciding between felt and synthetic underlayment? Each has its place, but the right choice depends on your project goals, budget, and climate conditions. Here’s a simple comparison to help you make an informed decision.

Criteria	Felt	Synthetic
Budget-Friendly	✅ Yes	❌ Higher cost
Water Resistance	❌ Lower	✅ Excellent
Tear Strength	❌ Prone to rip	✅ High durability
UV Resistance	❌ Degrades fast	✅ Holds up well
Ease of Installation	✅ Familiar and fast	✅ Lightweight and smooth
Long-Term Durability	❌ Shorter lifespan	✅ Built to last

Choose Felt if:

• You’re doing a quick repair, reroof, or temporary install
• Budget is tight and cost savings matter most
• Shingles or final roofing will be installed right away, minimizing exposure

Choose Synthetic if:

• You want maximum protection and long-term durability
• Your roof will be exposed to harsh sun, heavy rain, or high winds
• You’re building new, doing a full replacement, or investing in a premium system

In short, felt may work fine for temporary fixes or budget-driven projects. But if you’re aiming for reliability, durability, and weather resistance that holds up over time, synthetic underlayment is the better investment.

Whether you’re a homeowner planning a roof replacement or a contractor sourcing reliable materials, underlayment is one choice that shouldn’t be an afterthought. It’s the layer that quietly does the heavy lifting, protecting your investment from the elements day in and day out. Felt might get you by in the short term, but synthetic has become the go-to standard for anyone who values long-term durability and consistent performance.

Cutting corners here can cost you later. Make sure your roof has the protection it deserves. Reach out to your Trusted Roofing Expert for a free roof assessment and honest, expert advice.