There are three main types of sealing envelopes:

wet sealing (NK) sealing is triggered off by prior lubrication, which means that in order for the surfaces to be stuck together, all you need to do is to moisten the glue layer on the flap. If stored properly, this type of envelopes is characterised by unlimited life.

self-sealing (SK) - sealing based on latex. Both on the opening flap and the counter-flap there is a layer of glue. In order for the surfaces to be sealed, they must be pressed together. It is therefore particularly easy to seal manually. However, depending on storage, envelope life is restricted to one year.

self-sealing with a protective strip (HK) - this type of sealing is carried out by removing the strip protecting the glue layer, folding the flap, and pressing the envelope onto the flap. In this way it is tightly closed. Fast, secure, clean, practical, and comfortable. The main advantage of that the protective strip has over wet sealing or self-sealing is that it makes storage much easier, as the strip prevents the glue layer from sticking to envelopes stored beneath. In addition, this type of envelopes makes stuffing easier. Also, it is easier to keep the guarantee period of such envelopes, which is over 5 years. What is more, it is easy to print on this type of envelopes, as the protective strip on the opening flap prevents them from sticking to the printing machine.