Synthetic roofing paper is a woven or spunbond plastic underlayment, made from polypropylene or polyethylene, that rolls out over your roof deck before the shingles or metal go on. It replaces the older asphalt-saturated felt “tar paper,” and the two are not the same product despite the shared nickname. A single roll of synthetic covers about 10 squares (1,000 square feet), tears far less readily than felt, and sheds water rather than soaking it up. This guide explains what the material actually is, how to read its specs, what it costs, and how to pick a product, without rehashing the felt-versus-synthetic debate you can find below.
What is synthetic roofing paper?
Synthetic roofing paper is a factory-made plastic underlayment installed between the roof deck and the finished roof covering as a secondary water barrier. It is manufactured from polypropylene or polyethylene polymers, usually as a woven scrim laminated to a coated surface, and it carries no asphalt. “Paper” is a holdover term from felt; the modern product is closer to a technical fabric than to paper.
The layer does three jobs. It backs up the primary roof covering against wind-driven rain and any leaks that get past the shingles, it protects the deck during the days between tear-off and the finished roof going on, and it gives crews a walkable, marked surface to work on. It is not the same as the self-adhering ice and water shield used at eaves and valleys, which is a separate peel-and-stick membrane.
Because there was no single specification for years, products varied widely. That changed with ASTM D8257, the “Standard Specification for Mechanically Attached Polymeric Roof Underlayment Used in Steep Slope Roofing,” which sets floors for tensile strength, tear strength, water resistance, fastener pull-through, and surface traction. Older code-recognized felt specs, ASTM D226 (organic felt) and ASTM D4869 (asphalt-saturated felt), predate synthetics, so many synthetic makers still state that their product “meets or exceeds” those felt standards.
What is synthetic roofing paper made of?
Most synthetic roofing paper is built from polypropylene (PP) or polyethylene (PE), typically as a woven grid of plastic tapes bonded to one or more coated top layers. Polypropylene versions tend to be light with high tear resistance; polyethylene constructions add chemical resistance and dimensional stability. Some premium sheets add a fiberglass or spunbond reinforcement layer.
The surface treatment matters as much as the core. Manufacturers add a textured or gritted top coat for slip resistance, since bare plastic is dangerously slick when wet or dusty. Most rolls are printed with overlap lines and fastener-placement marks, which speed installation and cut layout errors. None of this exists on felt, which is a single asphalt-saturated mat.
Types of synthetic roofing paper
Synthetic roofing paper splits into three broad classes: standard mechanically fastened sheets, high-performance or self-adhered sheets, and breathable underlayments. The right class depends on your roof covering, slope, and climate, not on price alone. The table below sets the practical differences side by side.
| Type | How it attaches | Best fit | Rough material cost / sq ft |
|---|---|---|---|
| Standard mechanically fastened | Cap nails or plastic-cap staples | Most asphalt shingle reroofs | $0.15 to $0.30 |
| High-performance / heavy synthetic | Cap nails, higher tear and UV rating | High-wind zones, long exposure windows | $0.25 to $0.45 |
| Self-adhered synthetic | Peel-and-stick, no fasteners | Low slope, valleys, tile, some metal | $0.40 to $1.00 |
| Breathable (vapor-open) synthetic | Cap nails | Unvented or vapor-sensitive assemblies | $0.25 to $0.50 |
Breathable products are the outlier worth flagging. Standard synthetics carry a very low perm rating, often under 0.1 perms by ASTM E96, which makes them a near vapor barrier. Breathable synthetics run 12 to 20 perms so moisture can escape upward. On a poorly vented or unvented deck, a non-breathable sheet can trap moisture, so the choice is an assembly decision, not a preference.
How to read the specs on a synthetic underlayment
Four numbers separate a job-grade synthetic from a bargain sheet: tear strength, weight, perm rating, and the exposure (UV) rating. Manufacturers publish all four, and reading them keeps you from paying premium price for felt-grade performance. Each spec below is a concrete, comparable figure.
- Tear strength (ASTM D4533). Look for 15 pounds minimum; 25 pounds or higher is preferred for wind and foot traffic. Felt commonly tears well below this.
- Weight per square. Synthetics run roughly 4 to 6 pounds per square (100 sq ft) versus 15 to 30 pounds for #15 or #30 felt. Lighter rolls mean fewer trips up the ladder and larger coverage per roll.
- Perm rating (ASTM E96). Under 0.1 perms is effectively waterproof and non-breathable; 12 to 20 perms is a breathable product. Match this to your ventilation.
- UV / exposure rating. Stated in months, commonly 3 to 12 months. This is how long the sheet can sit exposed before the covering must go on. Felt often fails within hours to days in sun.
How much does synthetic roofing paper cost?
Synthetic roofing paper costs roughly $0.15 to $0.45 per square foot for the material on standard products, versus about $0.04 to $0.10 per square foot for #15 or #30 felt. On a typical 2,000 square foot roof, that is a material difference of a few hundred dollars, commonly $200 to $700 spread across the whole reroof. Self-adhered synthetics cost more, up to $1.00 per square foot.
Against a full replacement, the underlayment upgrade is small. On a $12,000 reroof, choosing synthetic over felt typically moves the total by about 2 percent. Labor often narrows the gap further: one roll of synthetic can replace several rolls of felt, so crews cover the deck faster with fewer seams. For a like-for-like look at the reroof numbers this rolls into, see the itemized tear-off pricing linked below.
How to choose a synthetic roofing paper
Choose by roof covering, slope, climate, and warranty requirement, in that order. Budget matters, but the material gap is small enough that spec fit should drive the decision. Work the list top to bottom and the right product usually names itself.
- Start with the roof covering. Metal and tile often call for specific underlayments; some metal jobs need a high-temperature or self-adhered sheet. Asphalt shingles accept most standard synthetics.
- Check the slope. Low-slope sections (typically under 4:12) usually need doubled coverage or a self-adhered membrane, per code and manufacturer instructions.
- Match perm to ventilation. Use a breathable synthetic on unvented or vapor-sensitive assemblies; a low-perm sheet is fine on a well-vented deck.
- Size the UV window to your schedule. If the covering may sit for weeks, pick a sheet rated for that exposure rather than a 3-month product.
- Confirm the warranty requirement. Top-tier system warranties from major shingle makers frequently mandate a synthetic underlayment from their own line, so check the covering warranty before you buy.
One rule holds across all of them: follow the manufacturer’s installation instructions for fastener type, overlap, and low-slope doubling. Warranty coverage and, in many jurisdictions, code compliance depend on it, and the requirements vary by product and by state.
For the full head-to-head on which material wins where, our felt vs synthetic underlayment comparison scores both across eight criteria. To see where synthetic fits among all the options, including peel-and-stick, start with our guide to roof underlayment types on the Learn hub. When you are ready to pick a specific product, our ranking of the best synthetic underlayment brands compares tear strength and price by product line. Because the underlayment sits directly on the deck, a soft or rotted deck must be handled first; see roof decking replacement cost. And for how this line item lands in a full quote, review our tear-off and reroof pricing.
Frequently asked questions
Is synthetic roofing paper the same as tar paper?
No. Tar paper, or felt, is an asphalt-saturated organic or fiberglass mat. Synthetic roofing paper is a woven polypropylene or polyethylene sheet with no asphalt. They serve the same role as underlayment, but synthetic is lighter, tears less, sheds water instead of absorbing it, and can sit exposed for months rather than hours. The shared “paper” nickname causes most of the confusion.
How long can synthetic roofing paper be left exposed?
Most synthetic underlayments are rated for 3 to 12 months of UV exposure before the finished roof must go on, and the exact figure is printed on the roll. Felt, by contrast, often degrades in sun within hours to a few days. Always follow the manufacturer’s stated exposure limit, since leaving any underlayment out past its rating can void coverage and let the sheet fail.
Does synthetic roofing paper need to breathe?
It depends on the assembly. Standard synthetics have a very low perm rating, often under 0.1, which makes them a near vapor barrier. On a well-vented deck that is fine. On an unvented or vapor-sensitive assembly, a breathable synthetic rated 12 to 20 perms lets moisture escape and helps prevent trapped condensation. Match the perm rating to your ventilation rather than defaulting to the cheapest sheet.
Is synthetic roofing paper worth the extra cost?
For most reroofs, yes. Synthetic costs roughly $0.15 to $0.45 per square foot versus $0.04 to $0.10 for felt, but that gap is only about 2 percent of a typical replacement. In return you get higher tear strength, a longer exposure window, and lighter rolls that install faster. Many manufacturer system warranties also require synthetic, so felt can quietly disqualify you from top-tier coverage.
What ASTM standard covers synthetic roofing paper?
ASTM D8257 is the specification written specifically for mechanically attached polymeric (synthetic) roof underlayment on steep-slope roofs. It sets minimums for tensile strength, tear strength, water resistance, fastener pull-through, and surface traction. Older felt standards ASTM D226 and D4869 predate synthetics, so many synthetic products state that they meet or exceed those felt specs in addition to D8257.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.