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

Here’s what I’ve seen, for what it’s worth:

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Sometimes I see wrinkles with felt if it’s gotten wet.

Bottom line for me: synthetic’s tougher and easier for shingle layout. Felt’s cheaper but way less forgiving if weather turns on you.

Had a flashback reading about the felt wrinkles - reminded me of a job a few years back where we got caught by one of those “20% chance of rain” afternoons. We’d just rolled out the felt, and by the time we got back the next morning, it looked like someone had tried to iron it with a potato. Ended up having to pull half of it up and start over. Not my favorite way to spend a Saturday.

I’ll give felt this: it’s cheap and easy to get, but man, you’ve gotta be lucky with the weather or move fast. Around here (humid summers, lots of pop-up storms), I just don’t trust it unless I know we’re shingling same day.

Synthetics are a different animal. They’re tougher than they look - had one sit exposed for almost two weeks when we hit a supply delay, and it barely budged. No wrinkles, no tears, just a little dusty. Only thing that gets me is how slick they can be in the morning. Nearly did a cartoon-style banana peel slip once - caught myself on the ridge vent and probably invented some new dance moves in the process.

One thing I’ve noticed: some of the cheaper synthetics can tear if you’re rough with them or if you’re working on a steep pitch and your boots catch an edge. But overall, I’d take that over felt any day for anything but the simplest jobs.

Installer skill’s huge too - seen plenty of “premium” underlayments botched by bad valley work or lazy nailing. Doesn’t matter what you use if water finds its way in.

If budget’s tight and weather’s perfect, felt can still do the trick. But for peace of mind (and fewer callbacks), synthetic wins out for me most days... even if my knees don’t always agree after sliding around on it all morning.

I get the appeal of synthetics, especially with unpredictable weather, but I’ve actually had felt hold up better on a couple older properties. Maybe it’s just luck, but after 10+ years under asphalt, the felt was still solid - no moisture issues. Synthetics are great for exposure, but I’ve seen some shrink or curl at the edges over time, especially with cheaper brands. That said, installer skill really is the wild card, like you mentioned:

“Doesn’t matter what you use if water finds its way in.”

- Totally hear you on installer skill being the wild card. Like you said,

“Doesn’t matter what you use if water finds its way in.”

Had a similar debate with myself last year when I redid my shed roof. Ended up going with felt because it was what I could get quick and cheap, and honestly, it’s held up fine so far. I did notice the installer thing is huge - my neighbor’s synthetic underlayment looked great until a windstorm peeled half of it back. Turns out the staples weren’t spaced right. I guess no matter what you pick, if it’s not put on right, you’re gonna have problems down the line.

You nailed it - installation really is half the battle. I’ve seen plenty of “premium” materials fail just because someone rushed the job or skipped a step. Felt’s been around forever for a reason, and if it’s holding up for you, that’s a win in my book. Sometimes the tried-and-true stuff just works, especially if you’re careful with the details.

Sometimes the tried-and-true stuff just works, especially if you’re careful with the details.

That hits home for me. I inspected a place last fall - original felt underlayment from the late 80s, still doing its job under some battered old shingles. Meanwhile, a newer house down the street had synthetic that started peeling at the edges after just five years. Both had decent materials, but you could tell who took their time on install. Makes me wonder if we sometimes overthink new tech when the basics are done right.

Funny, I’ve seen almost the same thing in my neighborhood. My place still has old-school felt from the early 90s - never had a leak, even after a couple nasty windstorms. Meanwhile, my cousin’s house (built 2017) had synthetic and he was patching it up after just a few years. I get that new materials have their perks, but sometimes it really does come down to how careful folks are during install. Maybe we’re just chasing “new” for the sake of it?

I get that new materials have their perks, but sometimes it really does come down to how careful folks are during install. Maybe we’re just chasing “new” for the sake of it?

I get where you’re coming from, but I’ve seen synthetic hold up better in a few cases, especially on low-slope roofs or spots that get a lot of sun. Felt can dry out and crack over time, especially if there’s poor ventilation. I do agree install matters a ton - seen plenty of “new” jobs fail because someone rushed it. But sometimes the newer stuff really does have an edge, depending on the situation.

I’ve pulled off a lot of old felt that was basically dust after 15-20 years, especially on south-facing slopes. Synthetics seem to handle heat and UV a lot better in my experience, though they can get slippery if you’re not careful during install. Still, I wouldn’t trust either one if the crew’s cutting corners... seen way too many shortcuts come back to haunt folks later. It’s a mix of material and workmanship, honestly.

Had a similar experience with felt turning into what looked like burnt toast crumbs on a teardown. Synthetics are definitely tougher, but man, I almost went skating off a roof the first time I walked on one after a rain. Still, if the crew’s rushing, doesn’t matter what you use - water finds every shortcut.

Synthetics are definitely tougher, but man, I almost went skating off a roof the first time I walked on one after a rain.

That’s exactly my worry with synthetics - one unexpected drizzle and it’s like an ice rink up there. Felt’s not perfect (the “burnt toast crumbs” description is spot on), but it at least gives you a bit more grip underfoot. Anyone tried recycled or plant-based options? Curious if they’re any less slippery or just as bad. I keep wondering if we’ll ever get an underlayment that doesn’t turn into either dust or a slip n’ slide...

I keep wondering if we’ll ever get an underlayment that doesn’t turn into either dust or a slip n’ slide...

I hear you. I’ve tried a couple of those recycled fiber mats - one from a local supplier, made with plant pulp and some kind of resin binder. They were definitely grippier than synthetics when wet, but they still broke down faster than I’d hoped, especially in our humid summers. Nothing’s perfect yet, but at least the eco options aren’t quite as slick underfoot. Still waiting for that “Goldilocks” underlayment myself...

Ha, “slip n’ slide” is right - my last go-round with synthetic underlayment was basically a backyard skating rink after a rain. I nearly did the splits hauling bundles up the ladder. I’ve been using felt for ages, mostly out of habit, but it’s not exactly built to last either. Down here in Georgia, the humidity just eats it up. I tried one of those “high-performance” synthetics and yeah, it held up longer, but walking on it in the morning dew was a gamble.

Funny enough, my neighbor swears by the recycled stuff too. He says it’s good for the environment and all that, but I watched him patching seams after just one summer. Maybe there’s some magic blend out there, but I haven’t found it. For now, I just pick whichever one won’t turn into confetti before the shingles go on. If someone invents an underlayment that doesn’t disintegrate or try to kill me, sign me up...

I hear you on the “skating rink” effect - first time I stepped onto synthetic after a rain, I nearly went down too. Here’s what I’ve figured out so far:

1. If you’re in a humid spot like Georgia (I’m in North Carolina, so pretty similar), felt just doesn’t last long if it’s exposed for more than a couple days. It gets soggy and tears up fast, especially if there’s any wind.

2. Synthetics are definitely tougher and lighter, but yeah, they can be slick as heck. I found that some brands have a textured surface that helps a bit, but it’s still not foolproof - especially with morning dew or pollen.

3. The recycled stuff is interesting, but I’ve seen seams curl up too. Maybe it’s better for low-slope roofs or sheds where you’re not walking on it much.

What’s worked best for me is getting shingles on as soon as possible, no matter what underlayment I use. If there’s any delay, I’ll tarp over the whole thing just to avoid the “confetti” situation you mentioned. Still waiting for someone to invent the perfect underlayment...

I’ve noticed the same thing with felt - if it’s humid or there’s a storm, it just falls apart way too fast. Synthetics are definitely more durable, but I’ve had crews complain about how slippery some brands get, especially in the early morning. I’m curious if anyone’s tried those newer “walkable” synthetics and actually found a difference? For now, I just budget extra time to get shingles on quick, but weather doesn’t always cooperate...

Synthetics are definitely more durable, but I’ve had crews complain about how slippery some brands get, especially in the early morning.

Yeah, those slick synthetics can turn a roof into a skating rink before the sun’s up. I’ve seen more than a few guys do the “morning slide.” Honestly, though, I still lean synthetic for longevity - felt just gives up at the first sign of humidity around here. The walkable stuff helps, but it’s not magic. At least you’re budgeting extra time... Mother Nature’s got her own schedule, as usual.

I’ve had both on my house over the years - old-school felt back in the day, and then synthetic when we re-roofed a few years ago. I’ll admit, the synthetic’s holding up better so far, especially with all the humidity and storms we get here in the Southeast. But that slipperiness is no joke; I watched my neighbor’s roofer nearly end up in his azaleas one chilly morning.

Has anyone noticed if certain brands are less slick than others? I’m wondering if it’s more about which product you pick than just “felt vs synthetic.” Also, for folks in colder or wetter areas, does felt ever hold up long-term? Around here it just curls up and tears after a couple seasons, but maybe it’s different out West or up North. Curious if climate makes a bigger difference than material sometimes...

- Definitely hear you on the slipperiness - synthetic can be like ice, especially early mornings.
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“I watched my neighbor’s roofer nearly end up in his azaleas one chilly morning.”

Not sure I’m totally sold on synthetic being the “safer bet” in the Southeast, even with all the moisture. Yeah, felt can break down faster in humidity, but I’ve seen some of these newer synthetics get brittle or curl up after a few years under metal - especially if there’s a lot of sun exposure. Maybe it’s just certain brands, but I’ve had callbacks where the underlayment basically turned into plastic wrap and started tearing at the fasteners.

Also, about slipperiness - gritty texture helps, but it’s still not great if you’re up there early or after a rain. At least with 30# felt, you know what you’re getting. It might not last as long on paper, but sometimes I’d rather deal with replacing felt every so often than risking a slip or having to rip up synthetic that failed weirdly.

Anyone else notice that some synthetics don’t breathe at all? Had a job last year where condensation built up underneath and caused more trouble than the old felt ever did. Maybe it’s just me being old school... but I’m not convinced synthetic is always better for every roof or climate.