Chunky vs. fine climbing chalk: which one actually holds longer?
Chunky holds longer. Fine coats faster but wears off sooner. That's the short answer, and it comes down to how each texture sits on your skin.
Fine powder is already broken down as small as it gets, so the moment it touches your hands, it's doing everything it's going to do. There's nothing left to release over time, which is why it feels great immediately and fades just as quickly, usually within the first few moves.
Chunky chalk works differently. A larger piece has more material still intact, so as it rubs against your skin through gripping and movement, it keeps breaking down gradually and releasing fresh chalk as you go. That's the mechanism behind why chunkier chalk tends to outlast fine chalk over the course of a session, it's not releasing everything at once.
Session (150g)
Session is an 80/20 blend, built to outlast. Fine powder coats your hands on the first dip, so the grip is there immediately. The chunky ...
Why doesn't everyone just use chunky, then?
Because chunky alone is slower to work in. Straight chunky chalk takes longer to coat your hands evenly right out of the gate, which is annoying if you want to chalk up and start climbing immediately. That's the tradeoff: fine coats fast and fades fast, chunky lasts longer but takes a beat to get going.
A blend gets you both. POUFF runs 80% chunky to 20% fine specifically to solve this, the fine portion gives you the fast initial coat, and the chunky portion is what's actually doing the work of lasting through the rest of your session.
Does this actually matter for how often you re-chalk?
It does. If you're re-chalking every move or two even on short problems, that's usually a sign your chalk is leaning too fine, either because that's how it's formulated or because it's already been worn down to powder in your bag. Chalk that's mostly chunky, or a blend weighted toward chunky, tends to need less frequent reapplication.
The takeaway
If longevity through a session is what you care about most, chunkier chalk wins, but a pure chunky chalk sacrifices how fast it coats your hands to begin with. A blended ratio is built to give you both ends of that tradeoff instead of picking one.