Tear Open a Sanitary Pad and Diaper Powder Falls Out?! The Secret of SAP Ratios

Tear open a sanitary pad and you'll find the same white powder as in a diaper. But there's less than a fifth of it. Why?

The powder is SAP — superabsorbent polymer. It drinks up water, and it goes into both diapers and pads.

The ratio is completely different

The secret is in the ratio. A sanitary pad is 10% SAP and 90% fluff pulp. A diaper, on the other hand, is over 50% SAP — thin diapers go as high as 70%.

Different liquid, different design

The reason is the liquid. Urine is watery, and 300–400 mL arrives all at once. The key job is the SAP swelling like a gel and locking it in.

Menstrual fluid, by contrast, comes in smaller amounts (30–40 mL total per cycle) and is viscous. So a pad's real job isn't absorbing — it's spreading. The pulp is designed to wick the thick fluid lengthwise across the pad.

That uncomfortable leak down the back when you stand up from a chair has an industry name: rewet. It happens when the spreading job fails.

3-line recap

1. The white powder in pads is the same SAP as in diapers, but under a fifth of the amount.

2. Pads: 10% SAP + 90% pulp; diapers: 50%+ SAP — different liquids, different designs.

3. Urine's job is "lock it in"; menstrual fluid's job is "spread it out." Fail, and you get rewet.

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The videos and illustrations in this post were AI-generated.

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