There are, of course, many types of face masks including those individuals make themselves but here we are concerned with medical face masks. Medical face masks have been designed to meet specific standards of performance.
There are two main categories, medical masks and respirator masks with a number of sub-categories.
Broadly speaking, medical masks are loose fitting (they still need to be worn properly to be effective) and protect the wearer for relatively large air borne particles. They can also others from the wearer secretions such as saliva. Some have protection against fluid penetration too.
Respirator masks are more precisely fitted masks (i.e. care needs to be taken when putting them on to make sure there is an effective “seal”). They additionally protect from much smaller particles including fluids which are filtered out by the mask.
Type II has a better level of filtration than type I.
Additionally, type IIR need to meet a specified level of protection against fluid penetration (types I and II are not required to meet fluid penetration standards).
These are standards applied to respirator masks.
FFP2 is a European standard, KN95 a Chinese standard and N95 a USA standard.
These are approximately equivalent standards but do differ somewhat in specific testing requirements.
This is the reference number of the European Standard for face masks (the current version at the time of writing is EN 14683:2019+AC:2019). This specifies what performance characteristics a mask must have.
The standard document specifies the, “construction, design, performance requirements and test methods for medical face masks intended to limit the transmission of infective agents from staff to patients during surgical procedures and other medical settings with similar requirements. A medical face mask with an appropriate microbial barrier can also be effective in reducing the emission of infective agents from the nose and mouth of an asymptomatic carrier or a patient with clinical symptoms.”