Porous materials aren't completely solid. They have tiny holes in their makeup called pores. This makes them lighter in density than nonporous materials. Common examples include skin, sponge pumice, and soil.
Some people also refer to things like borders as being porous. This means that passage in and out is possible because of holes in coverage. It can also be used to mean that something's leaky.
Definition of Porous
Porous materials contain small openings or holes in their composition. The structure includes cavities produced between the atoms that make up the rest of the material. Those cavities are commonly called pores. These materials typically have low density. They weigh less than nonporous materials.
Nonporous materials don't have pores. Examples include plastic, glass, and metal. They're higher density materials that lack all the little pockets of air you find in a porous material.
Porous Materials Mistaken for Nonporous Materials
There are some materials and hard surfaces that people assume are nonporous, but they require special coatings to resist moisture. Granite is a prime example. It's solid, and you don't see any little pores or holes. But It requires sealing to prevent moisture from damaging the stone. Wood is another example. If it's varnished, the sealant creates a nonporous surface. Without the sealant, wood has pores that would absorb moisture.
Examples of Porous Materials
Any material that has a void of space within its makeup can be considered porous. This void is a hole in the space otherwise taken up by the main structure of atoms that make up the rest of the material. Examples include the following:
Skin contains millions of pores. Many of the pores in skin aren't visible. They function by opening to allow skin to breathe, according to Healthline. They also contain a hair follicle and oil glands. You have a larger number of these glands in the pores on your chest, back, and face. That's why these pores often look like they're bigger than the pores on other body parts.
Did you know that the scientific name for sponges is Porifera. It means pore bearing. Sponges are covered in ostia. These are small pores that lead to canals and large holes and chambers within the sponge, according to Oceanic Research Group. Sponges feed by filtering liquid and capturing small particles. That's possible because of its porous nature.
Pumice is a type of igneous rock. It forms from molten lava during volcanic eruptions. When the lava cools, pumice takes shape. It has pores formed by gas bubbles that get trapped as the rock rapidly cools from its magma state. Some types of pumice have so many pores that it can float in water.
Soil is often described as being a porous material. The pores are open spaces between particles of soil. These openings are often formed by trapped gasses, rooting insects, and worm movements. Soil porosity is important because it contains groundwater and provides oxygen for plants.