3D printing shells are the outlines of each layer. They wrap the infill of the 3D entity. Depending on the settings of your slicer, you can customize your shells. Each layer has at least one shell.
Shell Thickness
There are two buttons next to Shell thickness, you can choose between two values, tracks or mm. The first option sets the number of shells and the second option sets the dimension of the shells. As for the latter, it’s a multiplier of the nozzle.
Enable Vase Mod
The object is divided into layers made up of only one shell. No inner nor outer infill, no top nor bottom. Just like a vase.
In the picture below, you can see the object with Vase Mode enabled.
The angle of Solid Surface fill
The upper and lower infill lines pattern can be changed. Setting it to 45°, standard-setting, the lines are perfectly slanting to the X and Y-axis.
Solid Fill Rotation per Layer
After each layer, the direction of the top/bottom layer gets switched, that’s the reason for the 90° number.
Solid Fill Rotation per Layer: 90°
Use concentric solid fill
Enabling this option, the upper and lower infill change in composition.
Notice, in the following picture, how it is concentric.
Horizontal Shell Thickness
Set the top/bottom layer thickness according to the function of the object.
Insideout perimeters
It’s possible to print the inner shells before than the outer ones.