Boolean Difference suppresses the thickness of a solid


I have a sphere of 4mm thick and I am trying to do a boolean difference with another solid.
However, after the boolean difference, the thickness of the sphere is null. Do you know why and what can I do to keep the thickness of the sphere ?
Thank You


can you upload the file or a image with the before and after situations? is not very clear what you have and what do you want.

Here are attached some pictures, I split the sphere in 2. Before the half sphere is full but after the boolean difference in the picture 2, the thickness has disappeared. Do you know how to keep the thickness ?

if you split the shpere, the clipping plane can’t show the thickness because is an open polysurface