The Shell operator allows you to give thickness to the faces of particle meshes, similar to how a normal Shell modifier works.
Outer amount: the distance to extrude faces along their normal.
Inner amount: the distance to extrude faces along the opposite direction of their normal.
Relative to surface area: the outer/inner amounts will be relative to the overall surface area of the particle divided by the set area.
Area: the set area to use in relative mode.
Open edges only: controls whether only elements with open elements are extruded.
Along vertex normals: extrudes faces along individual vertex normals.
Along average normals: extrudes all faces along the averaged normal direction of the whole mesh.
Specify X/Y/Z: extrudes faces in a specified direction.
None/Outer/Inner: controls which faces will be beveled.
Amount %: the amount of bevel to apply to the shell faces.
Outer MatID Enabled: controls whether outer faces are given a material ID override.
Outer MatID: the override ID to assigned to outer faces.
Inner MatID Enabled: controls whether inner faces are given a material ID override.
Inner MatID: the override ID to assigned to inner faces.
Edge MatID Enabled: controls whether edge faces are given a material ID override.
Edge MatID: the override ID to assigned to edge faces.
Select outer faces: flags outer faces for selection.
Select inner faces: flags inner faces for selection.
Select edge faces: flags edge faces for selection.
Generate edge UVs: controls whether UVs will be automatically generated for edge faces.
Size: the size of edge UVs.