Heavy Flow Menstrual Pants

Absorbency targets

Heavy flow is usually defined as 15–30 ml per change, though individual variation is wide. Buyers should specify:

• The test method (e.g. modified ISO 11948-1 or Edana WSP 242.2)
• The minimum acceptable result in grams
• Whether the test is run on a flat sample or on a curved chassis that mimics wear

A flat-plate test overstates real-world performance because fluid spreads differently on a curved body. Ask for a chassis test if possible.

Core engineering

Heavy-flow cores use one or more of these strategies:

• Higher SAP ratio. 50–65 % SAP by weight reduces bulk while maintaining fluid retention. The SAP must have high gel strength to prevent gel blocking.
• Dual-core construction. A narrow, high-density acquisition layer sits above a wider storage layer. This channels fluid to the centre and reduces side leakage.
• Raised leak guards. Standing cuffs of hydrophobic nonwoven contain lateral flow. The cuff height and elastic tension must be specified precisely.

Fit & coverage

Heavy-flow users need confidence during movement. Key fit points:

• Longer chassis. Front and rear extension reduce overflow at the waistband.
• Wider rear core. Fluid tends to pool toward the back when lying down; a wider rear pad catches this.
• Secure leg elastic. Gapping at the leg cuff is the main leak path. The elastic must maintain contact through walking, sitting and sleeping positions.

What to specify

• Absorbency test method and minimum result
• SAP brand, grade and ratio
• Core basis weight and construction (single, dual or channelled)
• Leak-guard height and elastic specification
• Chassis dimensions by size

Where heavy-flow products fail in use

Capacity is the number buyers ask for and the least useful one on its own. These are the four failures that actually get reported:

• Front saturation while the rear stays dry. Fluid arrives faster than the acquisition layer can spread it. Ask for acquisition time, and for the acquisition layer footprint relative to the core.
• Rewet under sitting pressure. Stored fluid returns to the surface when the wearer sits. Ask for rewet measured under load, not on a flat sample.
• Core break-up when wet. Pulp cores split under load and leak through the split. Ask for wet integrity or a wet tensile figure.
• Single-surge side leakage. One fast surge can exceed cuff capacity even when total capacity is adequate. Ask for a surge test, not only a capacity test.

Writing the RFQ line

"Heavy flow" is a marketing phrase, not a specification. Convert it into numbers before asking for a price:

• Assumed flow rate per hour and the surge volume per event you are designing for
• Absorbency target, plus the rewet limit you will accept
• Acquisition layer basis weight and core density
• Core length and width, and how far forward the core extends
• Standing cuff height
• Size curve and pack count

Claims you can defend on pack

Heavy flow is a positioning, not a measurement, and the claims built on it are the ones most likely to be questioned:

• Absorbency. State the figure in millilitres with the test method. A number alone cannot be compared with a competitor's number, and it cannot be defended if a retail customer asks how it was obtained.
• Wear time. Claims such as eight or twelve hours need a test of that duration. Few laboratories run one by default, so the protocol has to be agreed and documented, otherwise the number is an assumption rather than a result.
• Toxic shock warning. Some markets require a warning on absorbent hygiene products. Check the requirement for every destination before the artwork is finalised, because adding it later means reprinting packaging.
• Words to avoid. Medical grade, antibacterial and hypoallergenic all imply evidence and, in many markets, registration. If you do not hold that evidence, the word is a liability rather than a selling point.

The real risk with a high-capacity product is not capacity, it is rewet: fluid returning to the surface under body weight. Put a rewet limit in the specification and tell the user how often to change. A product marketed on absorbency without a change interval invites the very complaint it was designed to prevent.

Absorption speed and capacity

Heavy-flow buyers usually specify one number — total capacity in grams — and stop there. Capacity and speed are different properties, and a core can be excellent at one and poor at the other. Capacity is how much fluid the core retains under load; speed is how fast the first dose passes the topsheet and reaches the core. A high-SAP, thin core can post an impressive capacity figure yet let the first gush pool on the surface, which is exactly the failure a heavy-flow user notices.

• Capacity. State the method (modified ISO 11948-1 or Edana WSP 242.2), the result in grams, and whether the sample was flat or on a curved chassis.
• Speed. State the strike-through time in seconds, and ask for repeated strike-through — three successive doses of the same volume — because the first dose is always the fastest and the third is the one that leaks.
• Under load. Rewet measured after the core is loaded predicts comfort at hour four; dry capacity does not.

Acquisition layer design is what reconciles the two: an ADL spreads a gush across the core footprint so the SAP nearest the impact point does not gel-block and reject the rest. Light builds shipped without an ADL are the usual reason a high absorbency sample performs worse in wear than its capacity figure suggests. The method list is in absorbency testing.

RFQ line that works: capacity of at least X g by [method]; strike-through not more than Y s on the first dose and Z s on the third; rewet not more than W g after loading; all three measured on the same production build.

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