porosity

n. porousness, state of having many tiny holes

Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction.
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Noun
1. the property of being porous; being able to absorb fluids
(synonym) porousness
(antonym) solidity, solidness
(hypernym) consistency, consistence, body
(hyponym) sponginess

(n.)
The quality or state of being porous; -- opposed to density.
  

Degree to which soil, gravel, sediment, or rock is permeated with pores or cavities through which water or air can move.