This study shows the feasibility of clay reinforced alginate-based compartmented fibers as healing agent carriers for the autonomous healing of glass fiber reinforced polymer composites. First we report on the effect of montmorillonite (MMT) clay on the fiber tensile and vacuole lateral compression properties. It is found that the fiber tensile properties are enhanced with increasing MMT concentration, while the effects on the vacuole lateral compression properties are seemingly negligible. The second part of this work shows the proof of concept of healing by compartmented fibers in glass fiber reinforced polymer (GFRP) composites. A single- and a double-healing agent configuration, both based on epoxy–thiol chemistry, were compared in these model GFRP composites. The healing phenomena were quantified by mechanical characterization (interlaminar fracture and flexural testing) and nondestructive testing techniques (X-ray microtomography and air-coupled ultrasonic C-scanning). It is found that a configuration with one healing agent is favorable over a system with two separate agents and that further exploitation of the compartmented fiber concept should focus on the healing of matrix damage as the loss of mechanical integrity because of glass fiber fracture cannot be overcome. POLYM. COMPOS., 2017@en