There are product standards for a wide variety of protective clothing. These product standards describe the minimum technical requirements which PPE must satisfy.
Often a product standard makes a distinction between different levels of protection, these are called performance levels.
When manufacturers use EU harmonized product standards for the design of protective clothing and can demonstrate that it meets these requirements then the notified body where the application for EU type examination is laid down, see this as a 'suspected conformity'. This means that the product is approved.
A number of product standards also has provisions around the PPE marking. In some cases there are specific pictograms that are to be used. In most cases, it is necessary that the PPE is provided with the product standard(s) and any performance levels to be met.