1. Introduction:


Whatever style you wear this summer, you want it to be comfortable. And what is more cool and enduring than a cotton T-shirt you can accessorize to your hearts content. You may already have several T-shirts you cherish. But have you thought about the shirts UPF? That stands for ultraviolet protection factor, the standard rating system that tests and measures a fabrics ability to protect the skin from the initial onset of skin reddening caused by UN-B rays.


In this article we discussed the various factors, how to check the UPF (Ultra protection Factor of fabric) and importance of ultra protection of Apparels which we wear.


2. How to Calculate the Ultra protection factor of Fabric (UPF):


2.1: Testing Technique:


The transmission of ultraviolet radiation through a specimen is measured on a spectrophotometer or spectro radiometer at known wavelength intervals. The ultraviolet protection factor (UPF) is computed as the ratio of the erythemally weighted ultraviolet radiation irradiance at the detector with no specimen to the erythemally weighted UV-R irradiance at the detector with a specimen present.


The fabric have areas of different colors or structure, tests each color or structure if its size is sufficient to cover the measuring port.


Testing is done in two conditions:


a) Dry Evaluation

b) Wet Evaluation


a) Dry Evaluation


Place the specimen flush against the sample transmission port opening in the sphere. Make one UV transmission measurement with the specimen oriented in one direction, a second measurement at 0.79 rad (45) to the first and a third at 0.79 rad (45) to the second.


b) Wet Evaluation


Weigh the test specimen. Thoroughly wet out the specimen in distilled water by placing it flat in the bottom of a beaker and then pour distilled water into the beaker until the specimen is covered. Bring the wet pick-up to 140 5% by squeezing the wet specimen between blotting paper. Then proceed as above procedure to calculate the UV transmission.


 

2.2 Calculate the Ultraviolet Protection Factor (UPF) of each specimen using



2.3 Reporting of Results:


  • Total number of samples tested:
  • Solar Spectrum used:
  • UVA Average Transmission
  • UVB Average Transmission
  • Standard Deviation of UVA
  • Standard Deviation of UVB
  • UPF Value
  • Standard Deviation


3. Factors affecting UPF of the Fabric:


There are a number of factors that affect the level of ultraviolet protection provided by a fabric and the UPF rating. In order of importance these are: weave (tighter is better), color (darker is better), weight (also called mass or cover factor-heavier is better), stretch (less is better) and wetness (dry is better). The other major factor that affects protection is the addition of chemicals such as UV absorbers or UV diffusers during the manufacturing process. Many factors that make a garment comfortable also make it less protective.


UPF values


15 to 24 good sunburn protection

25 to 39 very good sunburn protection

40 to 50 excellent sunburn protection

 

It is also observe that after washing the UPF is increases pls find the reasons for the same are follow:


a)     Wash the sample once and it shrinks, decreasing the spaces between the fibers in the fabric. This tightening of the weave increases UV protection by increasing the cover factor, the surface area of the fabric covered by fibers.


b)     You can also wash the sample several times in most laundry detergent which will deposit optical whiteners on the cotton fibers. "The more washings a fabric undergoes, the higher the chemical build-up," There is some indication that washing fabrics in detergents containing fabric brighteners, which absorb UV radiation, might increase their protective capability.


Reference:


BSEN 13758-1 & AATCC 183 Standard test Method to determine the UPF of the sample.