What Is the Line Mask Tool in Blender?

The Line Mask tool in Blender is a specialized sculpting feature designed to quickly isolate sections of a 3D model using straight line gestures. By drawing a vector line across the screen in Sculpt Mode, artists can instantly mask off half of an object or create sharp, defined boundaries without needing to paint masks manually by hand. This article explains how the Line Mask tool functions, how to access it, and practical ways to integrate it into your 3D workflow.

Understanding the Line Mask Tool

The Line Mask tool operates in Blender's Sculpt Mode as part of the expanded masking toolset. Instead of brushing a mask onto a surface with a soft cursor, the Line Mask tool projects a straight cutting plane relative to your camera view. Everything on one side of the line becomes fully masked (protected from sculpting operations), while the other side remains unmasked and editable.

How to Use the Line Mask Tool

  1. Switch to Sculpt Mode: Select your 3D mesh and switch from Object Mode to Sculpt Mode.
  2. Select the Tool: In the left toolbar, click and hold the Mask tool icon, then select Line Mask from the pop-up menu (or press M to cycle through mask tools).
  3. Draw the Mask Line: Click and drag across the viewport to draw a line across your mesh.
  4. Position the Line: While dragging, hold the Spacebar to move the line to a new position before releasing the mouse button.
  5. Set the Mask Side: The shaded side of the line indicates where the mask will be applied. Releasing the click completes the operation.

Key Features and Settings

  • Orientation Sensitivity: The tool works in screen space. The angle of your camera view determines where the line projects through the 3D volume of the mesh.
  • Inverting the Mask: Once a line mask is drawn, pressing Ctrl + I inverts the selection, swapping the protected and active areas.
  • Clearing the Mask: Press Alt + M to clear all active masks on the mesh.
  • Adjusting Mask Softness: In the tool options panel at the top of the viewport, you can adjust the falloff setting to create either a sharp, hard-edged mask or a smooth gradient transition.

Primary Use Cases

  • Hard-Surface Sculpting: Creating perfectly straight panel lines, sharp bevels, or clean mechanical cuts on organic shapes.
  • Posing and Bending: Quickly isolating a limb or head at a specific joint line before using the Pose or Rotate tools.
  • Cloth Simulation Preparation: Defining strict, linear boundaries for the Cloth Filter tool to generate realistic folds against fixed edges.