Draw and merge paths with the Blob Brush tool

Use the Blob Brush tool to paint filled shapes that you can intersect and merge with other shapes of the same color.

The Blob Brush tool uses the same default brush options as calligraphic brushes. (See Calligraphic brush options.)

Path created with a Calligraphy brush (left); path created with the Blob Brush tool (right)

To see a video on using the Blob Brush tool, see ww.adobe.com/go/lrvid4018_ai.

When using the Blob Brush tool, keep the following guidelines in mind:

To merge paths, they must be adjacent in stacking order.
The Blob Brush tool creates paths with a fill and no stroke. If you want your Blob Brush paths to merge with existing artwork, make sure that the artwork has the same fill color and no stroke.
When drawing paths with the Blob Brush tool, new paths merge with the topmost matching path encountered. If the new path touches more than one matching path within the same group or layer, all of the intersecting paths are merged together.
To apply paint attributes (such as effects or transparency) to the Blob Brush tool, select the brush and set the attributes in the Appearances panel before you start drawing.
You can use the Blob Brush tool to merge paths created by other tools. To do this make sure that the existing artwork does not have a stroke; then set up the Blob Brush tool to have the same fill color, and draw a new path that intersects all of the paths that you want to merge together.

Remember that paths with strokes cannot be merged.

Select the path into which you want to merge a new path.
In the Appearances panel, deselect New Art Has Basic Appearance. When this option is deselected, the Blob Brush tool uses the attributes of the selected artwork.
Select the Blob Brush tool , and make sure it uses the same appearances as the selected artwork.
Draw paths that intersect with the artwork. If the paths don’t merge, check to make sure that the Blob Brush tool’s attributes exactly match the existing path attributes, and that neither uses a stroke.

Double-click the Blob Brush tool in the Tools panel and set any of the following options:

Keep Selected: Specifies that when you draw a merged path, all paths are selected and remain selected as you continue to draw. This option is useful for viewing all paths that are included in the merged path. When you select this option, the Selection Limits Merge option is disabled.
Selection Limits Merge: Specifies that if artwork is selected, the Blob Brush merges only with the selected artwork. If nothing is selected, the Blob Brush merges with any matching artwork.
Fidelity: Controls how far you have to move your mouse or stylus before Illustrator adds a new anchor point to the path. For example, a Fidelity value of 2.5 means that tool movements of less than 2.5 pixels aren’t registered. Fidelity can range from 0.5 to 20 pixels; the higher the value, the smoother and less complex the path.
Smoothness: Controls the amount of smoothing that Illustrator applies when you use the tool. Smoothness can range from 0% to 100%; the higher the percentage, the smoother the path.
Size: Determines the size of the brush.
Angle: Determines the angle of rotation for the brush. Drag the arrowhead in the preview, or enter a value in the Angle text box.
Roundness: Determines roundness of the brush. Drag a black dot in the preview away from or toward the center, or enter a value in the Roundness text box. The higher the value, the greater the roundness.