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

I get the old school appeal, but I gotta say, I went with synthetic on my shed last fall and it was a game changer.

“on a smaller job where you’re not leaving it exposed for long, felt still seems like the safer bet.”

“it didn’t wrinkle up when it rained, which always drove me nuts with felt.”

That’s a big one for me too. I’ve seen felt turn into a soggy mess after just one surprise storm, especially if you’re not getting shingles on right away. But I do wonder - on bigger roofs or in high-wind areas, does synthetic ever get slicker to walk on? I’ve had a couple close calls where the felt actually gave me more grip, weirdly enough.

I’m in tornado alley, so storm damage is kind of my hobby at this point. After one hailstorm, the synthetic underlayment on my neighbor’s place held up fine even though half his shingles were shredded. Meanwhile, another buddy with old-school felt had water sneaking in through nail holes. Not saying synthetic is bulletproof, but it seems to bounce back from abuse better.

Still, I get the “overkill” argument for smaller jobs. Sometimes you just want to slap something down and move on. But if you’re worried about storms or delays, synthetic’s peace of mind is hard to beat... even if it costs a bit more up front.

I’ve noticed the same thing with synthetic - great water resistance, but it can get a bit slippery, especially if there’s morning dew or dust. On steeper pitches, I’m extra careful. Felt does seem to have more grip underfoot, at least until it gets soaked. For me, the trade-off is worth it since synthetic holds up better during those inevitable weather delays... but yeah, footing isn’t always ideal.

I’ve had to weigh this exact trade-off on a few different buildings, and honestly, I keep coming back to synthetic for the long haul. The water resistance is just hard to beat, especially when you’re dealing with unpredictable weather or delays in getting shingles down. I get what you’re saying about the footing though - on a steep pitch, that slickness can be nerve-wracking. We had a crew slip on a frosty morning last fall, and it was a wake-up call to double-check safety protocols.

Felt does have that grippier feel underfoot, at least until it gets saturated. But in my experience, once it’s soaked through (which happens fast in heavy rain), it starts to tear and wrinkle. That’s led to more headaches than I care to remember - especially if the roof sits exposed for more than a day or two. Synthetic just seems to hold up better if there are any delays or if you’re juggling multiple projects at once.

One thing I’m still not totally sold on is how some synthetics handle UV exposure. Some brands claim they’ll last months uncovered, but I’ve seen them start to degrade or get brittle after just a few weeks in direct sun. Maybe that’s just our Texas heat talking... Has anyone actually left synthetic exposed for an extended period and had issues? Or is that mostly marketing hype?

Also curious if anyone’s run into warranty problems with either type - some manufacturers seem picky about what counts as “proper installation.” It’d be good to know if felt or synthetic has caused more headaches with claims down the line.

At the end of the day, I lean toward synthetic for durability and weather resistance, but footing and install safety are real concerns. Wondering if there’s a brand out there that’s found a way to balance both?

- Had to pick between felt and synthetic for my own roof last year (asphalt, moderate pitch, Midwest weather).
- Went with synthetic because we had a week of rain delays and I didn’t want to risk leaks.
- Noticed it was a bit slick when I walked on it, but I just took it slow and wore shoes with good grip.
- Left it exposed for almost three weeks - no issues, but it wasn’t blazing hot here like Texas.
- Warranty stuff is confusing... My installer said as long as you follow the nail pattern and overlap rules, you’re usually fine. Haven’t had to file a claim (yet), fingers crossed.
- For my budget, the peace of mind with synthetic was worth the extra cost. If you’re worried about footing, maybe check if any brands have a textured surface?