The bag is guided into the heating section (either by hand or by machine) where there are heating bars on each side. These heating bars transfer heat into the bag and melt the material together. If the machine has a cooling section, the bag is then guided through the cooling section.

The "STP" terminology applies to sealing all different types of bags and film:

S - Speed. This is the speed the bag is traveling through the machine or the number of bags sealed per minute.

T - Temperature. This is the temperature of the heating bars.

P - Pressure. This is the amount of pressure which is applied to the bag as it goes through the heating section.

To seal a bag each parameter must be present, however, the settings may vary depending on the type of bag, the number of bags to be sealed (bags per minute), and the type of sealer (Impulse or Band). For instance a 1 mil. (100 gauge or 1/1000 of an inch) thick polyethylene (soft film) bag seals easily and will require less heat and pressure applied than a 1 mil. thick laminent, or using the same STP settings, you could run the polyethylene bag at a faster rate than the laminent.

Polypropylene is a "hard film" and is also known as "supported". Due to the fact that it is a hard material, it takes more heat and/or pressure to seal the bag.