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

Thing is, I’ve heard mixed stuff - some people say synthetic can get brittle in extreme heat (I’m in Texas, so, yeah). Felt seems tried and true but maybe doesn’t last as long?

I totally get the overwhelm. I went through this last year with my own roof (asphalt shingles, Houston area). Ended up going with synthetic since the contractor swore by it, but honestly, I was nervous about the heat too. After two brutal summers, it’s still holding up fine - no weird curling or cracking that I can see from the attic. My neighbor stuck with felt and had some minor leaks after a storm, but he also has an older roof pitch. If you’re watching costs, felt is cheaper upfront, but I figured the extra for synthetic might save me headaches later. It’s a toss-up, but I don’t regret going synthetic so far.

If you’re watching costs, felt is cheaper upfront, but I figured the extra for synthetic might save me headaches later.

I’ve managed a handful of properties around Dallas and Austin, and honestly, I’ve seen both hold up and both fail, depending on the install. Synthetic’s definitely gotten more popular with the roofers I work with, but I’ve had a couple of them mention that not all synthetics are created equal. Some of the cheaper brands apparently do get brittle or even sort of “powdery” after a few years of Texas sun, especially if there’s any delay getting shingles on top. But the better stuff seems to last.

Felt’s kind of old school, but I get why folks still use it. It’s cheap, and if you’re just looking to get a few more years out of an older roof, it’s not a bad call. That said, I had a rental in San Antonio where the felt basically melted into the decking after a few 100+ degree days - made repairs a pain later.

One thing I haven’t seen mentioned much is how long the underlayment is exposed before shingles go on. Had a crew leave synthetic uncovered for almost two weeks during a busy season, and it held up fine. Not sure felt would’ve survived that.

Curious if anyone’s had issues with warranties? I’ve heard some shingle manufacturers want synthetic underlayment for their longer warranties now, but I haven’t dug into the fine print. Anyone run into that? Or is it just marketing?

Had a crew leave synthetic uncovered for almost two weeks during a busy season, and it held up fine. Not sure felt would’ve survived that.

That’s been my experience too - synthetic just seems to handle the sun better if there’s any delay. I’ve seen felt basically bake onto the decking in the summer, which is a nightmare if you ever need to pull it up. As for warranties, you’re right, some shingle brands are picky now. I had to double-check specs on a hail job last year because the manufacturer only honored their warranty with a certain synthetic underlayment. It’s not always just marketing, unfortunately.

Had a similar debate a couple years back when I had to replace a section of roof after some wind damage. I went with synthetic on the advice of the roofer, mostly because they said it’d hold up better if there were delays (and there were, thanks to rain). Haven’t had any issues with it getting brittle so far, but I do wonder how it’ll look in another 10 years. For what it’s worth, the felt underlayment on the older part of the roof was pretty much toast - crumbled apart when we pulled the shingles. Maybe that’s just Texas summers for you.

That’s interesting - when you said,

“the felt underlayment on the older part of the roof was pretty much toast - crumbled apart when we pulled the shingles,”

I get why everyone’s jumping on the synthetic bandwagon, but I’m not totally convinced it’s the clear winner long-term, especially in places with crazy heat like Texas or Oklahoma. The stuff definitely holds up better than felt when you’re working on it - no tearing, doesn’t soak up water if you get caught in a storm mid-job. But I’ve seen a couple of older synthetic installs where the material started curling up at the edges or got weirdly brittle after a decade or so. Maybe it’s the brand or just bad luck, but it makes me wonder if it’s as bulletproof as people say.

Felt isn’t perfect, but at least you know what to expect - yeah, it’ll break down eventually, but it’s been around forever and it’s predictable. Synthetic’s still kind of new in the grand scheme. I guess time will tell if it really beats felt by a mile or just by a few years. Either way, Texas sun is gonna wreck whatever you put up there sooner or later...

I’m in North Texas and went with felt last time just because it was cheaper, but now I’m starting to wonder if I should’ve spent the extra for synthetic. My neighbor’s roof got redone two years before mine with synthetic, and his still looks fine, but it’s only been about 8 years total. I do worry about the sun breaking down anything up there - my old felt lasted maybe 16 years before I had to patch a few spots. For me, it came down to price and what my roofer was comfortable with. If synthetic lasts longer, great, but I’d hate to pay more upfront just to have it curl up or get brittle like you mentioned.

I’m in DFW too and had the same debate last year. Ended up with synthetic because my roofer swore it’d hold up better in our heat, but honestly, I still wonder if it’s worth the extra cost. Anyone else notice synthetic gets super slick when wet? That made me nervous during install.

Anyone else notice synthetic gets super slick when wet? That made me nervous during install.

That’s a legit concern. I was on a crew last summer in Arlington, and the first rain after we rolled out the synthetic, it was like walking on ice. The grip is way worse than felt, no question. We started using those slip-resistant shoe covers, but even then, you’ve gotta be careful. If you’re DIY-ing or just up there checking things out, it’s something to think about.

As for how it holds up in DFW heat - synthetic definitely doesn’t wrinkle or break down as fast as felt when it’s baking in the sun all day. Felt can get brittle and tear if you leave it exposed too long, especially if there’s a delay with shingle delivery or weather stalls the job. I’ve seen felt basically melt into the decking after a week of 100+ temps.

But yeah, the price difference is real. Synthetic can run double or more what 30# felt costs per roll. The trade-off is you’re getting something that’s lighter to haul up (seriously, your back will thank you), and it usually comes in wider rolls so you cover more area faster.

One thing to watch for: not all synthetics are created equal. Some of the cheaper brands don’t seem much tougher than heavy-duty plastic sheeting, and they can tear around fasteners if you’re not careful. The higher-end stuff has better UV resistance and doesn’t rip as easily.

If I had to pick for DFW specifically, I’d lean synthetic for longevity, but only if you’re not worried about the budget. For a quick patch or a rental property where cost matters more than lifespan, felt still works fine - just don’t leave it uncovered for long.

And yeah, always check the traction before stepping out after rain... learned that one the hard way.

- Totally agree about the slipperiness. I've seen more than one contractor nearly take a spill on synthetic after a rain.
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“Felt can get brittle and tear if you leave it exposed too long, especially if there’s a delay with shingle delivery or weather stalls the job.”

I get why everyone’s leaning synthetic these days, but honestly, I’ve seen felt outperform some of the cheaper synthetics when it comes to nail sealing and overall grip - especially on steeper pitches. Yeah, felt can bake if left out too long, but if you’re moving quick or have a smaller job, it’s less of a worry. Plus, I’ve noticed some synthetics get brittle in cold snaps and start to crack around fasteners. Not saying felt’s perfect, but I wouldn’t write it off completely for every situation.

That’s interesting about the cold snaps making synthetics brittle - I didn’t even think about that. I’m in Michigan, so we get some wild temperature swings, and my old felt underlayment actually held up better than I expected. The only thing that bugged me was when it got soaked and wrinkled up a bit before we got the shingles down. Has anyone had issues with synthetic getting slippery or tearing during install? I keep hearing it’s “tougher,” but I’m not totally sold yet...

I’ve used both and honestly, synthetic does get slick - especially if there’s any frost or dew. It’s tougher in terms of tearing, but I found it way harder to walk on safely. Felt’s not perfect, but at least I felt more stable up there.

I get what you’re saying about synthetic being slick - had a crew nearly wipe out on a frosty morning last fall. We switched to felt for the rest of that job just to play it safe, even though it tears easier if you’re not careful. But honestly, I’ve noticed synthetic seems to hold up better if there’s any delay between underlayment and shingles, especially with all the rain we get here. Felt can get soggy and start curling up if it sits too long.

Curious if anyone’s had issues with synthetic breaking down from UV exposure? I’ve heard mixed things - some say it’ll last weeks uncovered, others say it gets brittle fast in direct sun. Never had that problem with felt, but then again, we try not to leave anything exposed longer than we have to. Anyone actually seen synthetic fail from sun damage, or is that just talk?

- Seen a few synthetics get brittle after a couple weeks in direct sun, especially the cheaper brands.
- Most of the time, though, they hold up better than felt if you’re stuck waiting on shingles.
- Felt definitely curls and gets soft if it rains, like you said.
- I’d just check the manufacturer’s UV rating - some are only good for a week, others claim 60 days, but I wouldn’t push it that long.
- You’re not alone - lots of folks have the same concerns. Just gotta weigh the trade-offs for your job and weather.

Gotta say, I’m still a bit old-school and lean toward felt for most jobs, especially if you know the shingles are going on quick. I get the whole “synthetics hold up better” thing, but I’ve seen some of those fancy rolls turn into potato chips after a week of Texas sun. Like you said,

“Seen a few synthetics get brittle after a couple weeks in direct sun, especially the cheaper brands.”

I get where you’re coming from - felt’s definitely more forgiving if it gets wet, and it’s familiar. But I’ve had the opposite experience with synthetics, especially the higher-end ones. On a couple of big projects last summer, we had synthetic underlayment exposed for almost three weeks in 100+ degree heat, and it held up fine. I do think you hit the nail on the head with this:

“especially the cheaper brands.”

I hear you on the cheap synthetics - some of that stuff is basically glorified plastic wrap. But man, the good brands are a different animal. We had a roll of felt basically melt into the deck one July, but the synthetic next to it looked like it just came out of the package. I still keep a roll of felt around for small jobs, but for anything that’s gonna sit exposed, I’m not risking it anymore.

We had a roll of felt basically melt into the deck one July, but the synthetic next to it looked like it just came out of the package.

That’s exactly what happened to me last summer. We had a stretch of 95+ days and I swear, the felt was basically glued to the plywood by the end of it. I had to scrape it off in strips, which was not how I planned to spend my Saturday. The synthetic stuff right next to it? Looked untouched, like you said. I’m starting to think felt just can’t keep up with these crazy heat waves.

I still use felt for patch jobs or small repairs, mostly because it’s cheap and I’ve got a few rolls left in the shed. But for anything that’s gonna sit exposed for more than a day or two, I’m with you - synthetic all the way. The only thing that bugs me is some of the synthetics are so slippery. Nearly did the splits trying to walk across one last fall. If anyone’s got a trick for not sliding around on that stuff, I’m all ears.

One thing I’ll say for felt, though - it’s way easier to cut and lay flat, at least for me. Some of those synthetics curl up at the edges and fight you every step of the way. But I guess that’s a small price to pay if it’s not going to turn into roof lasagna in the sun.

Curious if anyone’s had luck with those “premium” felts they sell now? Supposedly they’re more heat-resistant, but I haven’t tried them yet. For now, I’m just glad my last big job didn’t end with me peeling felt off like old wallpaper...