Blisters appear as swellings on the surface of the paint and vary considerably in both size and density. Coarse blisters, larger than 1.5 mm in diameter, generally occur in patches.
Water droplets impacting on, and evaporating from, the surface.
The marks may result from:
Dewax the affected area, flat lightly, compound and polish, repeating if necessary. In severe cases repaint the topcoat.