Which holds up better over time: felt or synthetic underlayment?

I get the appeal of synthetic, especially with all the rain some areas get, but I’ve actually had decent luck with good old felt on a few properties - one’s pushing 15 years and still holding up fine (asphalt shingles, moderate slope, Pacific Northwest). It does come down to the install, though. If the crew rushes or cuts corners, even the fanciest underlayment won’t save you from leaks.

That slickness you mentioned with synthetic is no joke. Had a crew slip on one of my jobs too, and it definitely slowed things down. Also, I’ve noticed that if there’s a delay between underlayment and shingles (weather, scheduling, whatever), felt seems to handle UV exposure a bit better short-term. Synthetic can get brittle if it sits exposed too long.

Not saying one’s always better than the other - just depends what you’re willing to trade off. For me, I still lean felt for smaller jobs or where I know I’ll be able to keep up with regular maintenance. But yeah, if you want to forget about it for 20 years, synthetic’s probably safer.

It does come down to the install, though. If the crew rushes or cuts corners, even the fanciest underlayment won’t save you from leaks.

This is so true - it’s wild how much hinges on the actual install, not just the product. I get why folks stick with felt, especially for smaller jobs or when you know you’ll be up there keeping an eye on things. But honestly, I’ve seen way too much felt end up in landfills after 10-15 years, and it’s not exactly biodegradable. That’s one of the reasons I lean toward higher-end synthetic underlayments - some are made from recycled materials now and last longer before needing replacement.

I totally hear you about synthetic getting slick. I’ve been on roofs where it felt like skating on ice, especially if there’s a little dew in the morning...not fun. But if you’re thinking long-term and want to minimize waste (and headaches), synthetics do seem to hold up better - assuming install isn’t rushed and you’re not leaving it exposed for weeks.

It’s all trade-offs, like you said. For me, the environmental angle tips it a bit toward synthetic these days, but I wouldn’t fault anyone for sticking with what’s worked for them - especially in wet climates like ours.

Yeah, I’ve had that “skating rink” moment on synthetic too - nearly lost my dignity (and my hammer). For me, the big win with synthetic is how much lighter it is to haul up a ladder, especially solo. But I do miss how felt sort of “grips” the deck, especially on steeper pitches. If you’re careful with install and don’t leave it baking in the sun for weeks, synthetic seems to last longer in our rainy climate. Still, I keep a roll of felt around for patch jobs or quick fixes...old habits die hard.

I hear you on the synthetic “ice rink” effect - had a crew member end up sliding halfway down a 10/12 last year. Not fun to watch. The weight difference is a real game changer though, especially when you’re moving materials up three stories. I’ll admit, there’s something about the way felt sort of settles in and grabs the sheathing that’s reassuring, especially on those steeper slopes.

That said, I’ve noticed synthetic holds up better for us during construction delays. Had a project where the roof sat open for almost a month during the rainy season (not ideal), and the synthetic was still solid when we finally got back to it. Felt would’ve been mush by then. Still, for quick patch jobs or when I need something that’ll just “stick” and not blow around, I reach for felt too. It’s tough to let go of old habits, and sometimes the tried-and-true stuff just feels right.

Honestly, both have a place, depending on the situation and the weather you’re up against. Your point about not letting synthetic bake in the sun rings true - seen it get brittle if it sits too long. Just comes down to what you trust for each job, I guess.

- Had a similar situation with synthetic -

“synthetic ‘ice rink’ effect - had a crew member end up sliding halfway down a 10/12 last year.”

That “ice rink” feeling with synthetic is no joke - I’ve nearly lost my footing more than once. I get why folks like it for durability, but honestly, I trust felt way more on steep slopes. You nailed it though, depends on the job and weather. Both have their headaches.

That “ice rink” feeling with synthetic is no joke - I’ve nearly lost my footing more than once.

I know exactly what you mean. I was up on a 10/12 pitch last fall, and the synthetic felt like walking on a greased slide after a light frost. Made me rethink my footwear choices, honestly. Have you noticed any difference in how either holds up after a few years? I’ve seen some older felt jobs that looked rough, but then again, I’ve also seen synthetic start to curl at the edges in heavy sun. Wonder if climate plays a bigger role than we think...

I get the concern about synthetic curling in the sun, but honestly, I’ve seen felt get brittle and basically disintegrate after a couple summers baking on a hot roof. Around here (humid summers, cold winters), synthetic seems to last longer if it’s covered up quick, but if it sits exposed, yeah, it can start to curl or even tear at the fasteners. Felt’s more forgiving if you’re working in cooler temps, though. I’m not convinced there’s a clear winner - it really depends on how long it’s exposed and what kind of weather you’re dealing with.

I’ve seen the same thing - felt just can’t take prolonged heat, especially on low-slope roofs where water sits. But synthetics aren’t perfect either. If you’re not careful with fasteners or you leave it exposed too long, wind can rip it right up. Around here (Midwest), I lean synthetic for most jobs, but only if we’re shingling within a week or two. Otherwise, felt’s still got its place, especially in cooler months when it’s less likely to dry out and crack.

“But synthetics aren’t perfect either. If you’re not careful with fasteners or you leave it exposed too long, wind can rip it right up.”

That’s the kicker, isn’t it? I’ve had synthetic underlayment turn into a kite on a windy day - looked like a scene from The Wizard of Oz. Here’s my step-by-step: if I know the crew’s coming quick, I’ll go synthetic for sure. But if there’s any chance of rain delays or the job dragging out, I stick with felt. It’s heavier and less likely to end up in my neighbor’s yard. In winter, felt seems to hold up better too... less curling and cracking. Just gotta watch those seams, or you’ll be chasing leaks later.

“I’ve had synthetic underlayment turn into a kite on a windy day - looked like a scene from The Wizard of Oz.”

Been there, done that, and nearly lost my hat in the process. Synthetics are great when you’re moving fast, but if the weather’s got other plans, you’re basically rolling out a welcome mat for the wind. I’ve seen more than one neighbor’s yard decorated with my underlayment after a surprise gust.

Felt’s not perfect either, but I agree - it just sits heavier. Especially in cold snaps, it doesn’t get all brittle and weird like some synthetics do. Down here in the Midwest, we get those “four seasons in a week” stretches, and felt seems to ride it out better if things get delayed.

That said, if you’re roofing in the summer and can get shingles on quick, synthetics are lighter on the back and don’t soak up water like felt does. But yeah... leave it exposed too long and you might as well be chasing tumbleweeds. Just depends how fast your crew is and what the forecast looks like.

“you’re basically rolling out a welcome mat for the wind.”

That’s the truth. I’ve had synthetic flap around so much it sounded like a marching band up there. If you’re expecting any kind of delay, felt’s just less drama. But if you can shingle same-day, synthetic saves your back - no contest.

I get what you’re saying about the wind, but honestly, I’ve had felt tear and bunch up after a couple days of rain and sun before I could get shingles on. Synthetic’s slipperier, but it didn’t fall apart on me. Maybe it depends on the brand or how you tack it down?

“I’ve had felt tear and bunch up after a couple days of rain and sun before I could get shingles on. Synthetic’s slipperier, but it didn’t fall apart on me.”

That’s been my experience too, especially when the weather flips back and forth. Felt just doesn’t handle the elements well if it’s exposed for more than a day or two. I’ve seen it wrinkle up and even rip right around the fasteners after a heavy downpour, which is a pain if you’re waiting on inspections or just get hit with a stretch of bad weather.

Synthetic is definitely slicker to walk on, which can be sketchy, but it’s held up way better for me when jobs get delayed. I wonder if part of it is how tight you stretch it or the type of cap nails you use. Some brands of synthetic seem tougher than others, though - one time we used a cheaper roll and it actually tore at the seams when we were dragging bundles across it. Still, I’d take that over felt getting soggy and useless.

Maybe in a dry climate felt would last longer, but around here (Midwest), with all the rain and humidity, synthetic just seems less hassle in the long run.

I hear you on the felt turning into a soggy mess - nothing like coming back after a weekend of rain to find it looking like a used tissue. I’ve had it tear right at the staples too, especially if the wind picks up. Synthetic’s definitely more forgiving if you get stuck waiting for an inspector or the weather decides to play games.

But man, that stuff is slippery. I swear, I’ve done my best Olympic skating routine on synthetic more than once. Anyone else notice some brands are way worse than others? I had one roll that was basically an ice rink, but another with a little grit wasn’t so bad. Maybe it’s just luck of the draw.

I do wonder if stretching it tighter helps, or if it just makes the seams want to pull apart faster. And don’t get me started on those cap nails - if you don’t use enough, even synthetic will flap around in a good storm.

Honestly, unless you’re roofing in the desert, felt just seems like asking for trouble these days. But hey, maybe someone out there’s had better luck with it?

I hear you about the slipperiness - nearly took a dive myself last fall. My experience is synthetic holds up better long-term, especially in wet climates, but it really does depend on the brand. Some have a gritty texture that helps, others are like skating on glass. I’ve tried stretching it tighter, but honestly, if you overdo it, you end up with seams that pull apart when temps swing. Cap nails are a pain but worth it if you don’t want to find your underlayment halfway down the street after a storm. Felt just doesn’t seem to stand a chance around here with all the rain and wind we get.

Cap nails are a pain but worth it if you don’t want to find your underlayment halfway down the street after a storm.

That line made me laugh - I've seen more than one job where the underlayment ended up in the neighbor's yard after a windy night. I agree, synthetic tends to outlast felt around here (Pacific Northwest, so rain is basically a given), but I've also noticed some brands get brittle after a few years of sun exposure. Had one inspection last spring where the synthetic was practically crumbling, but the felt on a different section was still hanging on. Maybe depends on how much direct sun your roof gets?

Had one inspection last spring where the synthetic was practically crumbling, but the felt on a different section was still hanging on.

I've run into this too, especially on south-facing slopes where the sun just bakes everything. It's weird - synthetic is supposed to be tougher, but I've seen it get brittle and almost flake apart after a few years of direct exposure. Meanwhile, old-school felt sometimes just keeps chugging along, even if it's a bit ragged.

One thing I've noticed is that not all synthetics are created equal. Some of the cheaper brands seem to break down way faster, especially if they're left exposed for more than a couple weeks before shingles go on. Around here (western WA), the rain is relentless, but when we do get sun, it can be brutal on materials that aren't UV-rated.

Curious if anyone else has seen felt outlast synthetic in certain spots? Or maybe it's just a fluke with specific brands or install methods. Either way, I always check for brittleness during inspections now - never used to worry about that with felt.

Yeah, I’ve seen felt outlast synthetic more than once, especially when the synthetic’s been left exposed too long. Honestly, I’m not convinced all these “new and improved” synthetics are actually better - some of them just seem like glorified plastic tarps. The sun here in Texas will chew through the cheap stuff in no time. Felt might look rough after a while, but at least it doesn’t turn into confetti when you touch it. Maybe it’s just me, but I trust the old black paper more than some of these mystery-brand synthetics.

I get where you’re coming from - felt just seems to do its job, even when it’s looking a little ragged. We bought our place last year (central Texas), and I spent way too much time reading up on all the underlayment options before we finally got the roof redone. The roofer actually tried to push a “premium” synthetic, but I kept thinking about how brutal the sun gets here. Like, if that stuff starts breaking down before the shingles even go on, what’s the point?

Here’s what I ended up doing:
1. Asked for samples of both felt and synthetic and left them out in the backyard for a week. The synthetic started curling at the edges and got kind of brittle. The felt looked rough but held together.
2. Talked to a couple neighbors who’d done roofs in the last five years. One guy had a synthetic underlayment, and he said it was fine... until he had to patch a leak and realized it basically shredded when he tried to lift any shingles.
3. Called my insurance rep to see if they cared which one I used (they didn’t, as long as it was code).

In the end, I went with 30-lb felt. It was cheaper, and at least I know what to expect if I have to make any repairs later. If you’re not sure about the new synthetics, I don’t think you’re alone. Maybe some of them are better for really steep roofs or super-windy places, but for regular asphalt shingles in this heat, old-school felt just makes sense.

Not saying synthetics are all bad - some folks swear by them - but unless you’re getting one of the top-tier brands (and paying for it), I’d rather stick with something that’s proven itself over time. Plus, like you said, nothing worse than having your “upgrade” turn into confetti after a single Texas summer.