We're finishing our basement and need to figure out insulation before drywall goes up. Right now it's just concrete blocks with moisture issues in one corner. Should we use fiberglass batts, rigid foam, or spray foam? Also worried about vapor barriers.
The moisture corner is actually your biggest clue here - before you pick any insulation material, you need to figure out where that water's coming from and stop it at the source, or you're just putting a band-aid on the problem. Once you've dealt with drainage or sealed cracks, closed-cell spray foam works great for basements because it blocks moisture AND provides decent R-value in a thin layer, but if budget's tight, rigid foam boards (XPS or polyiso) are nearly as good and way cheaper - just make sure you tape all the seams and install a proper vapor barrier on the warm side. Fiberglass is honestly the wrong call down there like the other answer said, but I'd skip the fancy encapsulation systems unless water's actively pooling; sometimes good gutters and grading outside solve half your problem for free.
Rigid foam or spray foam is gonna be your best bet for basements, especially with those moisture issues you mentioned. Fiberglass batts absorb water and'll fall apart if they get wet, which isn't worth the risk. Spray foam seals everything up tight and acts as its own vapor barrier, so you don't need to worry about that separately. Before you insulate anything though, fix that damp corner first - could be drainage, a crack, or a hydrostatic pressure problem. Once that's sorted and the walls are dry, rigid foam boards are cheaper and easier to install yourself, while spray foam gives better air sealing if you're willing to pay more.
Interior drain tile or a sump pit might be what you're actually missing - that moisture corner won't stay dry just because you slap insulation over it, and you'll end up with mold behind whatever you install. Once you've dealt with the water source (whether it's grading, gutters, or an actual drainage system), spray foam is solid for basements because it blocks moisture and seals gaps, but rigid foam works too if budget matters and you're diligent about sealing seams with tape. The vapor barrier question depends on which route you pick: spray foam acts as its own barrier, but rigid foam usually needs one on the warm side. Just don't assume the insulation itself is going to solve a water problem - that's what gets people into trouble.
You've got to stop that moisture first or nothing else matters - I dealt with a similar corner in my place and found out the gutters were dumping water right at the foundation! Once I fixed the drainage outside, I was able to actually insulate properly. Spray foam or rigid foam boards are solid choices, but they won't save you if water keeps creeping in. Get that corner investigated and sorted before you buy a single sheet of insulation, or you'll be ripping everything out in a couple years!
Spray foam is gonna be your workhorse here, but the moisture thing really does come first. Everyone's right that water's the enemy - I had a similar wet corner in my own basement and waterproofed it from the outside before touching any insulation. Turned out a downspout was redirecting water straight into the foundation. Once that was fixed and the corner stayed dry for a few months, I felt confident about insulating. Spray foam gives you an air seal plus insulation in one shot, which matters because basements leak air like crazy otherwise.
For the actual install, closed-cell spray foam is pricier but handles moisture way better than open-cell. You spray it right onto the concrete, and it creates its own vapor barrier as it cures - no separate membrane needed. Just make sure you're using it correctly (get a pro if you're unsure) because bad application can trap moisture between the foam and the block. After that dries, you've got a solid thermal break and sealed wall. Rigid foam boards work too if budget's tight, but they need more careful sealing at seams and edges to avoid cold spots and condensation.
Foam insulation is definitely the right call for basements, and everyone here is spot on about the moisture issue being your real problem. That corner won't magically dry out just because you add insulation - it'll trap moisture and breed mold behind your walls. Get down there and trace where the water's actually coming from first. Could be gutters, grading around the foundation, or interior seepage. I had a similar situation a few years back and discovered my downspout was essentially creating a small river right at the foundation line. Once I redirected that, the dampness cleared up.
That said, assuming you can actually get the water source under control, spray foam or rigid foam panels both work well because they don't absorb water like fiberglass does. Spray foam gives you better sealing and air-tightness, which is nice. Rigid foam is easier to install yourself and less messy. With either option, you'll want a vapor barrier on the warm side of the insulation (the interior), but honestly if you're dealing with active moisture, the barrier only matters once you've fixed the underlying problem. If that corner stays damp, no barrier will save you.
Once you've sorted the moisture problem (and everyone's right that you have to), consider installing rigid foam directly against the concrete and then furring out the wall with thin strips before drywall - this gives you an air gap that helps with any residual dampness and makes the whole assembly more forgiving than foam-right-to-drywall. Skip the vapor barrier on the inside; with rigid foam already blocking moisture transmission, you don't need one and it can actually trap water that sneaks in from cracks. The real hack nobody mentioned is sealing all those concrete block voids with hydraulic cement first - water loves finding its way through tiny gaps in the mortar, and it's way easier to patch before insulation goes in than to rip everything apart later if you missed a spot.
Before you touch any insulation, seal that concrete with a waterproofing coating (liquid applied stuff like Drylok works fine) once you've confirmed the water source is actually external and not rising damp from below the slab. After that's cured, rigid foam board is your move - it won't absorb moisture like fiberglass, and you can tape the seams to create a semi-continuous vapor control layer without needing a separate plastic sheet. The one thing that doesn't get mentioned much: install a capillary break between the slab and your framing by laying down some closed-cell foam or rigid board directly on the concrete before your rim joists go down, since moisture can wick up from the floor and ruin everything above it.
Spray foam will actually seal air leaks better than rigid foam and handles that damp corner more forgivingly, but everyone's right that you need to track down where the moisture is coming from first - otherwise you're just trapping it behind new material.
Skip fiberglass batts down there - they're basically sponges waiting to fail! I had the same setup at home and went with closed-cell spray foam because it handles moisture way better than rigid foam and actually seals air leaks, but here's the real talk: that wet corner is screaming at you to fix the water problem first. Check your gutters, grading around the foundation, and whether you need interior drainage before you spend money on insulation, or you'll be tearing it all out in a couple years dealing with mold.
Have you actually confirmed where the water's coming from - is it seeping through the concrete or coming from above? Either way, everyone's right that moisture is the real enemy here, but I'll add this: even after you fix the source, spray foam or rigid foam with a proper vapor barrier beats fiberglass because it handles any residual dampness without deteriorating, and you get better air sealing as a bonus.
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