Disposable underpads look simple — a rectangular absorbent sheet. But the difference between a pad that leaks through in two hours and one that holds through the night is in how each layer is built. For hospitals, nursing homes, and home care distributors, getting this right means fewer bed changes, less skin breakdown, and lower overall cost per patient-day.
The Four-Layer Structure
Standard disposable underpads use four functional layers. Each plays a specific role:
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Topsheet (Layer 1): Nonwoven fabric, typically spunbond polypropylene at 15–18 gsm. Its core function is to allow rapid liquid penetration while maintaining a dry surface touch. Premium-grade underpads adopt quilted or embossed patterns to accelerate liquid diversion from the surface and avoid local liquid accumulation.
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Acquisition and Distribution Layer (Layer 2): Composed of airlaid paper or cellulose tissue, this layer evenly spreads incoming liquid across the entire absorbent core area. Without this layer, liquid will pool locally, resulting in inefficient absorption of the underlying SAP (Super Absorbent Polymer) and greatly reducing the pad’s overall liquid-holding performance.
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Absorbent Core (Layer 3): A composite blend of fluff pulp and SAP. Regular underpads generally contain 15–25% SAP by weight — lower than disposable diapers, as underpads are designed to absorb large-volume liquid dispersed over a wider area. Heavy-incontinence thickened underpads adopt a 30% SAP ratio with higher basis weight to meet super-absorption demands.
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Backsheet (Layer 4): PE film in common colors including blue, green and white, serving as the only leak-proof barrier to prevent liquid from seeping onto mattresses. The film thickness ranges from 18 to 25 microns. Films thinner than 18 microns are highly prone to pinhole defects during high-speed mass production, causing hidden leakage risks.
Key Performance Metrics to Verify
When comparing underpads from different manufacturers, focus on the following authoritative quantitative indicators to avoid subjective marketing exaggerations:
Total Absorbency Capacity
Measured in milliliters per single pad. A standard 60×90cm underpad features a conventional absorption capacity of 800–1500ml, which is determined by the SAP proportion and fluff pulp basis weight. It is recommended to require suppliers to provide official ISO 11948-1 test reports instead of informal marketing data.
Absorption Speed
Absorption speed is as critical as total absorption capacity. A pad with 1500ml maximum absorption but slow absorption cannot keep the surface dry. The industry high-quality standard requires absorbing 200ml of liquid within 10 seconds to keep patients dry in real-time use.
Dryness (Rewet Performance)
Rewet refers to the moisture that seeps back through the topsheet under external pressure after liquid absorption, a core index for assessing skin protection ability. Lower rewet values represent better surface dryness. For hospital-grade underpads, the optimal target is a rewet value below 0.5g after 500ml liquid absorption.
Common Quality Issues in Bulk Orders
Based on factory inspection and bulk order after-sales data, three recurring quality problems plague disposable underpad bulk shipments:
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Uneven SAP distribution: Inadequate mixing of SAP and fluff pulp during production leads to partial areas of the pad with almost no absorption capacity. If the SAP is treated with tracer agents in advance, this uneven defect can be clearly detected under UV light.
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Backsheet pinholes: Ultra-thin PE film is prone to microscopic pinhole damage during embossing, folding and other production processes. A simple post-production backsheet water drop test can effectively screen out defective products.
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Edge sealing failure: Fully sealed four edges are essential to prevent lateral liquid leakage. Unqualified heat sealing or ultrasonic bonding will cause edge leakage, which is the leading cause of product returns in bulk wholesale orders.
Sourcing Considerations for Wholesale Buyers
For full-container bulk procurement, buyers need to confirm the following key details with suppliers to stabilize product quality and avoid batch differences:
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Basis weight tolerance: Confirm whether the quoted GSM tolerance is ±5% or ±10%. A 10% tolerance for 100gsm pads will result in individual products as low as 90gsm, with a noticeable decline in absorption and durability.
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Packaging compression ratio: Excessive compression during export packaging will crush the fluff pulp structure, reduce bulkiness, and slow down liquid absorption. It is necessary to confirm the standard compression ratio of export packaging with suppliers.
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Certification consistency: Ensure that CE marking and FDA registration certificates correspond to the specific ordered SKUs, not just general factory certificates. Verify the certificate number through official databases to avoid invalid or mismatched certifications.
