How to Use Masks in After Effects

A workflow taught by Adobe Certified Instructors at Adobe Video World.

Masks are one of the most fundamental tools in After Effects, letting you reveal, hide, or isolate parts of a layer. Whether you’re cutting out an object, creating a reveal, or confining an effect to one area, masks make it possible. This guide covers everything from drawing your first mask to animating it across a shot.

What a Mask Does

A mask is a path you draw on a layer that controls which parts of that layer are visible. Everything inside the mask shows, and everything outside is hidden, so you can isolate a shape, an object, or a region of the frame. It’s the basic building block of compositing.

Unlike a shape layer, a mask doesn’t create new graphics — it modifies an existing layer’s visibility. That distinction matters: you draw a mask on the layer you want to affect, and it carves that layer down to just the area you’ve enclosed.

Draw a Mask with Shape Tools

The quickest way to make a mask is with the rectangle or ellipse tools. Select the layer you want to mask, choose a shape tool, and drag in the Composition panel to draw the mask directly onto that layer. The layer immediately shows only what’s inside the shape.

Hold Shift while dragging to constrain to perfect squares and circles, and double-click a shape tool to make a mask the full size of the layer. These simple shapes cover a huge number of everyday masking jobs without ever touching the pen tool.

Draw a Custom Mask with the Pen Tool

For anything that isn’t a simple rectangle or oval, the Pen tool lets you draw a custom path point by point. Click to place straight-edged points, or click and drag to create smooth curves that hug an object’s outline precisely.

Close the path by clicking back on your first point, and the mask is complete. The pen tool takes practice, but it’s the key to cutting around real-world objects, and our dedicated pen tool guide covers it in depth.

Understand Mask Modes

Each mask has a mode that controls how it combines with other masks on the same layer. Add is the default and shows the masked area, while Subtract cuts a hole, letting you create shapes like rings or frames from multiple masks.

Intersect, Lighten, and Darken give finer control when you stack several masks together. Combining an Add mask for the overall shape with a Subtract mask for a hole inside it is how you build complex selections that a single path couldn’t achieve.

Feather the Mask Edge

A hard mask edge looks cut-out and obvious, so soften it with Mask Feather. Twirl down the mask’s properties in the timeline and increase the Feather value to blur the boundary, blending your masked layer smoothly into whatever sits behind it.

Feathering is what makes a mask look natural and professional rather than pasted on. You can even feather one part of a mask differently from another using the Mask Feather tool, which is invaluable when an object has both sharp and soft edges.

Adjust Mask Expansion and Opacity

Two more mask properties give you everyday control. Mask Expansion grows or shrinks the entire mask outward or inward, handy for nudging a selection a few pixels without redrawing it. Mask Opacity controls how much the masked area shows through.

Lowering mask opacity lets the layer fade partially rather than disappearing completely outside the mask, which is useful for subtle vignettes and blends. Together with feather, these properties let you fine-tune a mask without ever touching the path itself.

Animate the Mask Path

Masks can move and change shape over time, which is essential for following an object. Keyframe the Mask Path property and reshape the mask on different frames, and After Effects animates the path smoothly between your keyframes — the foundation of rotoscoping.

This is how you keep a mask locked onto a moving subject, frame by frame. It’s painstaking on fast or complex motion, but it gives you total control when automatic tools fall short, and it’s a core visual-effects skill worth practicing.

Use Masks for Reveals

One of the most popular creative uses is a masked reveal. Animate a mask growing across a logo or title so it appears to wipe or draw on, a clean effect that’s perfect for lower thirds and brand animations.

By keyframing the mask path or expansion, you control exactly how and where the layer is revealed. Pairing a masked reveal with eased keyframes, as in our keyframe guide, produces the smooth, premium reveals you see in professional motion graphics.

Masks vs. Track Mattes

Masks and track mattes both isolate parts of an image, but they work differently. A mask is drawn directly on a layer, while a track matte uses a separate layer’s shape or brightness to define another layer’s transparency. Each suits different jobs.

Reach for a mask when you want to cut out or reveal part of a single layer, and a track matte when you want one layer to control another — like text revealing footage. Knowing which to use keeps your compositing clean and your timeline easy to follow.

Masking Best Practices

• Feather edges so masks blend naturally with the background.
• Use Add and Subtract modes together to build complex shapes.
• Keyframe the Mask Path to follow moving objects.
• Use Mask Expansion to resize a selection without redrawing it.

Common Mask Mistakes

• Hard, unfeathered edges that look obviously cut out.
• Drawing on the wrong layer instead of the one you want to mask.
• Forgetting to keyframe the path on a moving subject.
• Overcomplicating a selection that a couple of simple masks would solve.

Use Masks to Confine Effects

Masks aren’t only for cutting out layers — they also limit where an effect applies. Apply an effect like a blur or a glow to a layer, then draw a mask, and depending on the effect’s options the result confines to that region. This is how you blur one area or brighten just a subject.

Many effects include a Compositing Options section with an on-mask reference, letting you mask the effect directly. Combining masks with effects is a core compositing skill that, alongside adjustment layers in your wider workflow, gives you precise, targeted control over any part of the frame.

Smooth Mask Animation

When you animate a mask path across many frames, the motion between keyframes can sometimes feel mechanical. After Effects lets you refine this with mask interpolation and by adding more keyframes where the shape changes most. Smoother path animation reads as more natural, especially when rotoscoping a person.

For tricky shots, work in short spans and check every few frames rather than keyframing the whole clip at once. Patience here pays off, and the same careful, frame-by-frame discipline covered in our rotoscoping guide applies directly to animating any mask around a moving subject.

Key Takeaways

• Masks control which parts of a layer are visible.
• Draw them with shape tools or the pen tool for custom paths.
• Use mask modes, feather, and expansion to shape the selection.
• Animate the Mask Path to follow movement and create reveals.

Frequently Asked Questions

How do I create a mask in After Effects?

Select the layer you want to mask, choose a shape tool or the Pen tool, and draw a path in the Composition panel. The layer then shows only what’s inside the mask. Feather the edge for a natural blend.

What’s the difference between a mask and a shape layer?

A mask is drawn on an existing layer to control its visibility, while a shape layer creates new vector graphics. Use masks to cut out or reveal part of a layer, and shape layers to build graphics.

How do I animate a mask in After Effects?

Keyframe the Mask Path property and reshape the mask on different frames. After Effects animates the path between keyframes, letting the mask follow a moving object or create a reveal.

Sources: Adobe’s documentation on masks.