This study describes an innovative fiber technology with various applications, such as fiber-reinforced concrete (FRC), fiber-reinforced plastic (FRP), and plastic foaming. Unlike incumbent passive fiber reinforcing technology, in situ shrinking fibers that respond to an external stimulus such as heat, pH, or moisture variations can induce pre-compression to the matrix and create additional resistance from external loads, creating stronger composite structures. This new technology includes the design and fabrication of in situ shrinking fibers to improve performances in each application. Shrinking ratios and tensile strengths of fibers used in each application were measured. Specimens with active shrinking fibers, passive non shrinking fibers, as well as control samples have been made, and their performances have been compared. The first part describes the application of shrinking fibers in cementitious composite structures to provide supplemental strength-enhancing compressive stresses. Mechanical properties of the samples are compared with compression and three-point bending tests, using heat activated shrinking (HAS) fibers pH activated shrinking (pHAS) fibers. The second part describes the applications of through-thickness fiber reinforcement technology for polymeric laminate to provide supplemental strength-enhancing interlaminar stresses. To prove this concept, peel strengths of epoxy/glass fiber composite layers are measured. Also, in-plane tensile tests are conducted to investigate whether the through-thickness shrinking fibers affect in-plane properties. The third part demonstrates the application of shrinking fiber in improving foaming ability of linear polymers. The smart fiber blending technology would be able to tune the optimum degree of strain hardening behavior cost efficiently. The modification of the rheological properties by the fiber shrinkage is discussed. The extensional viscosity measurements are described in terms of strain-hardening behaviors in polymer composites containing shrinking fibers. Final foam properties resulting from these structures are also presented.