When we talk about the Ultraviolet Protection Factor (UPF) of fabrics, we're referring to the level of protection against sunburn-causing ultraviolet radiation (UV) that the fabric provides.
The UPF number itself describes the ratio of protection that the fabric gives, compared to no protection at all. So, if a piece of fabric is described UPF40, it means that for every 40 units of UV radiation that fall on the fabric, only one of them will pass through it. In other words, UPF40 fabrics have been tested to ensure that they block 97.5% of the UV radiation that falls on them.
This UPF is measured using an artificial light source. An algorithm that converts these results to realistically measure the fabric's "ability to protect against sunburn" across the relevant wavelengths (290-400nm) is then applied.
This is the general ASTM Standard for Sun Protective Clothing and Swimwear. It describes the UPF rating with a description of its corresponding level of protection.
Amount of UV radiation blocked
UPF < 24
UPF 25 – 39
UPF > 40
At Haglöfs, we only consider garments made with UPF40 fabric or higher to offer considerable protection against the sun. The UPF rating we give to our garments is a guideline, and - where applicable - we've labelled the clothing accordingly.
The rating is always given with the assumption that the fabric is of a medium to light shade, and that the fabric is dry and relaxed. If the fabric in the garment that the customer chooses is of a darker shade, then the UPF may well be similar or even higher as a result.
The UPF rating is given for fabrics that have not yet been used in the construction of a garment. While an item of clothing is being made, the material may be sewn, be stretched or otherwise altered in a way which impacts upon the UPF of the finished piece. UPF is also lowered:
Haglöfs products are not intended to be used for medical purposes. We do not take any legal responsibility if these guidelines turn out to be incorrect at any point.