GLOSSARY
Wall Thickness
Wall thickness (perimeter count) is how many loops of plastic the printer extrudes around the outside of each layer. Two perimeters is the default; three or four makes parts dramatically stronger.
Definition
Each layer of an FDM print is a stack of concentric outlines (perimeters or walls) plus interior infill. Wall thickness is either expressed as a count (e.g. 3 walls) or a measurement (e.g. 1.6mm with a 0.4mm nozzle = 4 walls). The slicer multiplies wall count by line width to fill the shell.
Why it matters
Wall thickness is the strongest determinant of part strength on FDM. Adding walls is more effective than adding infill, because the perimeters carry tensile load along the print direction and tie the layers together. A part with 4 walls and 15% infill is stronger than a part with 2 walls and 50% infill — and prints faster.
For visual prints, two walls (0.8mm shell) is fine. For functional parts, use three or four. For parts under significant load — hooks, brackets, hinges — five or more walls and oriented loading direction make a real difference.
Common confusion
Walls are not the same as infill. Infill is the lattice in the middle; walls are the solid shell. Increasing one does not replace the other — they reinforce different failure modes.
Top and bottom layers (sometimes called "solid layers") are a separate setting from walls. They control how thick the plastic skin is on horizontal faces, not vertical ones.