If underlayments had a race: which one would cross the finish line last?

- You’re not alone - lots of folks expect felt to help with attic temps, but once the shingles are on, airflow’s pretty much a non-factor.
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“the felt started curling and breaking down after about 7 years, especially where it got damp. The synthetics held up better, but they don’t ‘breathe’ at all.”

- That’s been my experience too. Synthetics just outlast felt, especially in humid climates. I’ve pulled up 5-year-old felt that looked 20 years old, while the synthetic stuff was still solid.
- Breathability sounds good in theory, but if water gets under your shingles, you’ve got bigger problems. Underlayment’s main job is to buy you time if there’s a leak, not to ventilate.
- Only spot I see breathability mattering is on old-school cedar shake roofs or something where the whole system is designed to dry out. For asphalt shingles in Georgia? Not so much.
- If you’re worried about trapped moisture, make sure your attic’s vented right. Underlayment can only do so much.
- Honestly, I’d take durability and tear resistance over “breathability” every time, especially with the storms we get down here.

- Synthetics definitely seem to “cross the finish line” way after felt, especially in humid spots.
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“the felt started curling and breaking down after about 7 years, especially where it got damp.”

- I’ve seen the same - felt just doesn’t hold up if there’s any moisture sneaking in.
- Only exception I’ve run into is on some old barns with cedar shakes, where breathability actually helped things dry out.
- Anyone here tried those newer “breathable” synthetics? Curious if they’re actually worth the extra cost or just marketing.

I keep hearing about these breathable synthetics, but honestly, I’m not sold yet. On paper, they sound like the holy grail - let moisture out, keep water from getting in... but does it actually work that way in real life? I’ve seen some of the older “breathable” housewraps trap moisture and cause rot, so I’m a little gun-shy. Anyone actually seen one of these synthetics hold up for 10+ years under real-world conditions? Or is it just another layer of expensive plastic that’ll end up in the landfill sooner or later?

I get where you’re coming from - some of those old “breathable” wraps were a joke. I’ve torn off roofs where the underlayment was basically mulch after a decade. But I’ve also seen newer synthetics hold up way better, especially on steep slopes. My uncle’s place had one of the newer brands under metal for 12 years now, and it still looked solid when we peeked during a repair. Not saying they’re perfect, but I wouldn’t lump all synthetics in with the early flops. Still, I’d trust good old felt in certain spots, especially on low slopes or tricky valleys.

If underlayments had a race: which one would cross the finish line last?

Honestly, I’ve seen felt hang in there longer than folks give it credit for, especially on my old ranch house. But yeah, those early “breathable” synthetics… might as well have used tissue paper. Newer synthetics seem tougher, but I still reach for felt if I’m patching a weird corner or a spot that stays damp. Costs less too, which never hurts.