ISO 9073-12 describes a method for the evaluation of the absorbency of fabrics when one side is in contact with a liquid and the fabric is under mechanical pressure.
This test is designed to allow comparison of absorbent materials such as nonwovens and is not intended to simulate in-use conditions of finished products.
Demand absorbency is also called demand wettability.
http://www.iso.org/iso/catalogue_detail.htm?csnumber=30169

There are several standard tests the industry uses to establish diaper absorbency. One is referred to as Demand Wettability or Gravimetric Absorbance. These tests evaluate what is commonly referred to as Absorbance Under Load (AUL). AUL is defined as the amount of 0.9% saline solution absorbed by the polymers while being subjected to pressure equivalent to 21,000 dynes, or about 0.30 lb/sq in (0.021 kg/sq cm). This test simulates the effect of a baby sitting on a wet diaper. If the diaper has an absorbency of at least 24 ml/g after one hour, the quality is considered acceptable.
http://www.enotes.com/how-products-encyclopedia/disposable-d...