It seems several people are packing the samples with the moisture content that results directly from the production line. Some clarification is necessary to enable you to obtain the results desired. The most important criteria in evaluating physical properties of substrates is to have a structure that does not change during testing. If your substrate is swelling or shrinking more than 3 mm above or below the top of the aluminum cylinder during the test, the numbers are not valid. There is NO structure in the bag or bale of product.
Structure is created by the end user.
Mixing of components Placing the substrate in the final flat, pot, basket, or other container Watering-in the substrate and allowing for initial settling. Growers and consumers can greatly alter the effective structure through handling and container selection. Here at the Horticultural Substrates Laboratory, we have tested thousands of samples including peats, barks, professional and consumer mixes. We have also evaluated many materials as perspective components. In all of our tests we try to evaluate structure as the plant would see it.