Off-contact is the gap between the bottom of the screen and the substrate (the item being printed). The purpose is to improve printability during screen printing process.
Please note that the off-contact is not the distance between the screen and pallet! It’s the distance between the screen and the garment, because the thickness of the garment can change. Therefore, you will have to tweak the position of the screen when you change from printing t-shirt to hoodies, raising it slightly to obtain the correct off-contact.
When you are printing garments use the thickness of a pound coin as a guide for the right off-contact. The goal of off-contact screen printing is to obtain a good “snap-off”, when the squeegee passes over the design the mesh will ping back creating a sharp crisp image.
Mesh tension also plays a role in the “snap-off”. If the screen mesh tension is between 15-20 newtons it’ll be just right. Any less and the mesh will be too loose to snap back into position.