The Hollowing blockers is a tool that allows the user to prevent the effect of the hollowing on some thin parts of the model for example. It’s available to pro users only.

Once in the Prepared Workspace with the Hollow Tool active on the left side, you will find a dedicated tool option for the Blockers on the right.

You will need to have one selected model with an object/all hollowing applied to be able to add/update the hollowing blockers.

When you press Add/Edit Hollowing Blocker you will start the process in a new window.

Select the most appropriate shape, cylinder, cube, sphere to start protecting your model.

Simply click on the surface to add a primitive and transform it using the gizmo to scale, rotate, translate operation.

Multiple primitives can be added if needed or duplicated using the dedicated button.

I needed a selected primitive can be deleted using the delete key or the red trash can icon.

When finished you can  update the result to apply the modification or exit without applying any modification. Make sure you update before leaving.

The hollow blockers visibility can be toggled between a wireframe view and an invisible state using the Show wireframe on/off switch.