In the past, we have been asked if the shade factor of a fabric also indicates how porous the fabric will be. If you’ve been asked this same question, or ever wondered if yourself, let us fill you in.
A fabric’s shade factor is the measurement of how much light will be blocked by the fabric. Due to this, many people think that shade factor also indicates how porous the fabric will be. Often times we are asked if a 50% shade fabric, for instance, will block 50% of water or air. At a high level, this would make sense, if shade factor was measured only by how much sun it physically blocks.
In fact, shade factor only includes the visible light blocked, and does not even account for UV blockage (UV rays are primarily absorbed by UV additives in the fabric). In a black fabric, a 70% shade fabric will provide 70% shade, meaning that 30% of the visible light will hit the surface(s) below the shade cloth. If using a colored fabric, the visible light blockage will be less, so a 70% white fabric will provide about 50% shade. This means that about half the light will hit the surface(s) below. Even though the construction of the 70% white is the same as the black, they do not block the same amount of light.
So does shade factor relate to porosity? Not necessarily.
Porosity relates to how much water or air can pass through a fabric. The denser a fabric is, the less air and water can pass through. For instance, a 30% knitted shade will allow more water and air to pass through compared to a 70% knit. However, that does not always mean that the construction equals porosity. Let’s take a look at two types of fabrics, knitted shade and woven shade. Even if both fabrics are made to block the same amount of light, the porosity may vary between the two. Why? The knitted shade has loops and knots throughout whereas the woven shade has a simple over-under construction. It would be easier for water or air to pass through the even pores of a woven shade than through the crisscross threads of a knitted shade. In a way, it can be thought of as how much friction the water would have as it tried to pass through the fabric. Think about a doorway. A smaller rectangle door is easier to pass through than a slightly larger door with a plank running diagonally across it.
While you could use the construction of a fabric as an estimate on how much water or air could pass through the fabric, it will not be as accurate as a formal test that will account for all factors.