Ask ten buyers what makes a good diaper and most will say "more SAP." The reality is more nuanced: super absorbent polymer (SAP) and fluff pulp work as a system, and core design matters as much as raw percentages. Here's how to read a core spec like an engineer.
What each material actually does
Fluff pulp is the sponge and the plumber. It wicks liquid away from the topsheet, spreads it across the core and holds it in suspension long enough for the SAP to absorb. High-bulk, soft fluff — like the North American pulp grades we use — also keeps the core comfortable against the skin.
SAP is the storage tank. It is a polymer that absorbs and locks liquid into a gel, under pressure, so it does not rewet. Sumitomo SAP, for example, is known for high retention and fast absorption. But SAP alone can't move liquid sideways — without pulp or an acquisition layer, liquid pools in one spot.
Why "SAP percentage" is not the whole story
- SAP quality varies — absorption speed, retention under load and gel strength differ between grades and suppliers.
- Distribution matters — an ADL (acquisition-distribution layer) pulls fluid deep into the core; without it, more SAP just means slower absorption in a wet spot.
- Balance beats maximum — a high-SAP core can feel stiff and take longer to absorb; the right pulp/SAP ratio gives fast take-in plus all-night retention.
What to ask your supplier
- Which SAP brand and grade does the spec use, and what are its retention and absorption-speed figures?
- Is there an ADL layer, and what is its basis weight?
- What are the lab results for rewet, absorption time and retention on this exact SKU?
A good core is engineered, not just loaded with polymer. That engineering is where the premium tiers earn their name — and where cheap cores usually cut corners.