Twin sheet forming and blow molding are both suitable for producing custom hollow plastic parts, but the choice between the two will depend on the specific requirements of the project. If the custom hollow plastic parts require a complex internal structure, varying wall thicknesses, and smooth surface finishes, then twin sheet forming may be the best option. However, if the parts require a simple geometry and a uniform wall thickness, then blow molding may be more appropriate. It is important to work with a manufacturer that has expertise in both processes to determine which one is best suited for your project.