The Acquisition Distribution Layer (ADL) in a disposable underpad sits between the topsheet and the SAP core. Its
engineering purpose is to spread liquid laterally across the core surface before it enters the SAP storage zone — preventing localized
saturation that causes surface wetness and premature leakage. A poorly designed ADL concentrates 80 percent of the liquid within a 10 cm
radius of the insult point, leaving 60 percent of the SAP core unused.
## H2: Bi-Component Fiber Geometry — The Foundation of Capillary Action ADL performance depends on fiber cross-sectional geometry, not just
grammage. Standard round polyester fibers have low capillary potential because they pack densely with minimal inter-fiber void space. Premium
ADL materials use bi-component fibers with eccentric sheath-core or side-by-side configurations. When thermally bonded, the two polymers
shrink at different rates, creating a three-dimensional crimp that produces large, interconnected capillary channels.
**What to ask the factory:** What is the fiber configuration in your ADL material — round, eccentric sheath-core, or side-by-side bi-component?
**Good answer:** Eccentric sheath-core PET/PE bi-component fibers at 40-55 gsm, with a minimum crimp frequency of 12 crimps per inch,
producing a void volume above 90 percent for rapid lateral liquid transport.
## H2: Strikethrough-to-Spread Ratio — The Metric That Matters Total absorbency is a misleading metric for underpads because it
measures static capacity, not dynamic distribution. The ratio that predicts real-world performance is the strikethrough-to-spread ratio:
how far the liquid travels laterally relative to how fast it passes through the topsheet. A ratio of at least 1.5 — meaning the liquid
spread zone diameter is at least 1.5 times the insult point diameter within 5 seconds — indicates effective ADL function.
**What to ask the factory:** What is the strikethrough-to-spread ratio for a 150 mL insult on your underpad ADL?
**Good answer:** Spread zone diameter of at least 15 cm within 5 seconds for a 150 mL insult (ratio above 1.5), verified by high-speed
video fluid-tracking analysis per production batch.
## H2: ADL-to-Core Interface and SAP Saturation Sequencing The ADL must deliver liquid to the SAP core in a controlled sequence —
not all at once. If the ADL dumps liquid too rapidly into a single SAP zone, that zone gels and blocks further absorption. The optimal ADL
design uses gradient density: higher fiber density near the insult point for rapid acquisition, transitioning to lower density toward the
pad edges for controlled release into the SAP core.
**What to ask the factory:** Does your ADL use a uniform or gradient density structure? How is the transition zone engineered?
**Good answer:** Gradient-density ADL produced by zoned through-air bonding — 50-55 gsm in the central acquisition zone, transitioning to
35-40 gsm in the peripheral distribution zone over a 5 cm gradient width.
## H2: Wet Collapse Resistance and Multiple-Insult Performance Standard ADL materials collapse when saturated, losing their
three-dimensional crimp structure and capillary function. This is why the second and third insults on an underpad perform worse than the
first — the ADL has become a flat, dense mat. Premium ADL materials incorporate a percentage of high-melt polyester fibers that retain
their crimp even when wet, maintaining capillary channels through multiple insults.
**What to ask the factory:** What is the wet collapse resistance of your ADL — measured as thickness retention after saturation?
**Good answer:** At least 70 percent thickness retention after saturation and a 2 kPa compression load for 10 minutes, achieved
through 20-30 percent high-melt PET fiber content in the ADL blend.
ADL engineering determines whether an underpad uses its full SAP core or wastes 60 percent of it through localized saturation. OEM buyers
who audit fiber geometry, spread ratio, gradient density, and wet collapse resistance will source underpads that perform reliably
through the complete nursing shift.
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Wholesome Hygiene — The Leading Disposable Hygiene Brand Since 1996. OEM/ODM manufacturing for adult diapers, pull-up pants, sanitary napkins, pet pads, maternity products, and more. Full customization, DDP logistics, and FBA support available.
