Blending modes for masks (mask modes) control how masks within a layer interact with one another. By default, all masks are set to Add, which combines the transparency values of any masks that overlap on the same layer. You can apply a mode to each mask, but you can’t animate a mask’s mode—that is, you can’t change a mask mode over time.

You choose a mask mode for a mask from the menu next to the mask name in the Timeline panel.

The first mask that you create interacts with the layer’s alpha channel. If that channel doesn’t define the entire image as opaque, then the mask interacts with the layer frame. Each additional mask you create interacts with masks located above it in the stacking order in the Timeline panel. The results of mask modes vary depending on the modes set for the masks higher up in the stacking order. Mask modes only operate between masks on the same layer.

Using mask modes, you can create complex compound masks with multiple transparent areas. For example, you can set a mask mode that combines two masks and sets the opaque area to the areas where the two masks intersect.

None

The mask has no direct influence on the alpha channel of the layer. This option is useful when you are only using the mask’s path for an effect such as Stroke or Fill, or if you are using the mask path as the basis for a shape path.

Add

The mask is added to the masks above it in the stacking order. The influence of the mask is cumulative with the masks above it.

Subtract

The influence of the mask is subtracted from the masks above it. This option is useful when you want to create the appearance of a hole in the center of another mask.

Intersect

The mask is added to the masks above it in the stacking order. In areas where the mask overlaps the masks above it, the influence of the mask is cumulative with the masks above it. In areas where the mask does not overlap with the masks above it, the result is complete opacity.

Lighten

The mask is added to the masks above it in the stacking order. Where multiple masks intersect, the highest transparency value is used.

Darken

The mask is added to the masks above it in the stacking order. Where multiple masks intersect, the lowest transparency value is used.

Difference

The mask is added to the masks above it in the stacking order. In areas where the mask does not overlap the masks above it, the mask operates as it would alone on the layer. In areas where the mask overlaps the masks above it, the influence of the mask is subtracted from the masks above it.