Synthetic vs. Felt Roof Underlayment: What’s the Difference?
Homeowners spend a lot of time choosing shingles.
Colour.
Style.
Warranty.
Brand.
But underneath those shingles is another layer that deserves attention:
Roof underlayment.
Envirotech’s current reroofing process includes preparing the roof deck and installing underlayment and flashing before the finished roofing material goes on.
Two common categories are:
traditional asphalt-saturated felt
and
synthetic underlayment.
They perform a similar basic role but are not identical.
What Is Roofing Felt?
Traditional felt uses an organic or fiberglass mat saturated with asphalt.
GAF describes it as an economical roof-deck protection material with a long history in residential roofing.
Common advantages include:
- Familiarity
- Availability
- Lower material cost
However, traditional felt can be:
- Heavier
- More vulnerable to prolonged weather exposure
- More slippery under some conditions
The specific product still matters.
What Is Synthetic Underlayment?
Synthetic underlayment generally uses polymers such as polypropylene or polyethylene.
GAF describes modern synthetic products as weather-resistant roof-deck barriers designed to provide protection beneath the final roofing.
Depending on the product, advantages can include:
- Lower weight
- Greater tear resistance
- Easier handling
- Better durability during installation
But “synthetic” does not describe one standardized product.
GAF specifically notes that synthetic underlayments can vary considerably between manufacturers.
Is Underlayment Waterproof?
Don’t confuse general underlayment with dedicated self-adhering leak barriers.
Underlayment adds protection.
Ice-and-water membranes are specifically designed for higher-risk areas such as eaves and valleys.
They are related components—but not automatically interchangeable.
Which One Is Better?
There isn’t one answer for every roofing system.
The correct choice can depend on:
- Shingle manufacturer
- Roof slope
- Warranty requirements
- Exposure conditions
- Product specification
- Local requirements
The most important issue is compatibility with the complete roof system.
Why Homeowners Should Ask About It
Once your roof is finished, you probably won’t see the underlayment again.
That is exactly why it belongs on the quote.
Ask:
- What underlayment are you using?
- Who manufactures it?
- Is it appropriate for the shingle system?
- Where will self-adhered leak protection be used?
- Is it included in the roofing warranty requirements?
The Shingles Are What You See. The Underlayment Is Part of What Protects Them From Below.
When comparing roofing quotes, Envirotech Exteriors can explain the complete roof assembly—not simply the colour and brand of the shingles on top.