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

Has anyone noticed a difference in attic temps or ventilation between the two? Wondering if that matters much.

I’ve been up in a lot of attics after both felt and synthetic installs, and honestly, I haven’t seen much of a difference in attic temps or ventilation just from underlayment choice. Ventilation’s more about your soffit and ridge vents than what’s under the shingles. Synthetic’s tougher in storms for sure - seen felt rip right off in a bad wind, but never noticed it changing attic heat one way or another.

I’ve always leaned toward synthetic for durability, especially here in the Midwest where storms can get wild. Like you said, I’ve seen felt peel up or even disintegrate after a few wet/dry cycles, while synthetic just hangs tough. But I do wonder if anyone’s noticed issues with synthetic getting slick during install? Some of my crew have complained about footing, especially on steeper pitches.

As for attic temps, I agree - never really noticed a difference tied to underlayment. It’s all about airflow and insulation up there. What I have seen is felt starting to wrinkle or buckle if it gets soaked before shingles go on, which can make the finished roof look a little off. Curious if anyone’s had long-term issues with synthetic breaking down under shingles after 10+ years? Haven’t torn off enough old synthetics yet to say for sure…

I hear you on the synthetic getting slick - my neighbor’s crew had a guy slip last fall, so it’s definitely a thing. Still, I’d rather deal with that than felt turning to mush after a week of rain. Haven’t seen any old synthetics fail yet, but I’m watching too.

- Price was my main reason for sticking with felt last time - synthetic was almost double at my local yard.
- But yeah, after two bad storms, the felt started curling up and I had to patch it.
- Haven’t tried synthetic myself, but I’m wondering if it’s worth the extra up front.
- Anyone notice a difference in how long the synthetic actually lasts before you need to reshingle?
- Midwest weather here - lots of freeze/thaw, if that matters.

But yeah, after two bad storms, the felt started curling up and I had to patch it.

That’s exactly what pushed me toward synthetic the last time we did a roof. The upfront cost stings, no argument there, but I’ve seen way fewer call-backs for leaks or repairs since making the switch - especially after those freeze/thaw cycles you mentioned. Has anyone actually had felt last more than 7-8 years in Midwest winters? I’m curious if it’s just our area, or if others are seeing the same thing.