| http://www.w3.org/ns/prov#value | - The intermediate layer can be different (i.e., harder or softer) than the core layer with a hardness difference of at least 1 unit in Shore A, C, or D, such as at least 3 units, or at least 5 units, or at least 8 units, or at least 10 units, or less than 20 units, or less than 10 units, or less than 5 units.
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