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How to use mask expansion in After Effects

Mask Expansion grows or shrinks the mask without moving individual points — perfect for tightening edges quickly without rebuilding the shape.

Steps to use mask expansion

Select your layer and press MM to open Mask properties.

Mask Expansion property visible in the After Effects timeline

Adjust Mask Expansion — positive values expand outward, negative values contract inward. The shape stays the same, it just offsets outward or inward from where you drew it.

Adjusting the mask expansion value to increase mask size in After Effects

Preview with different Feather amounts to balance softness and overall size.

Composition viewer in After Effects showing a feathered mask enlarged using Mask Expansion

One more thing

Animate Mask Expansion to create simple reveals without touching the path at all — keyframe it from a negative value to 0 or positive and it grows smoothly.

Related how-tos

How to feather a mask in After Effects
How to animate a mask path in After Effects
How to combine masks with add and subtract in After Effects

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