Access to computer-aided fabrication tools, such as 3D printing, empowers various craft techniques to democratize the creation of artifacts. To afford new blow molding techniques in the field of Human-Computer Interaction, we make efforts to simplify this challenging handy fabrication and enrich the design space of blow molding by taking advantage of the thermoformability and heat deformability of 3D printed thermoplastics. We propose a novel and democratized blow molding technique, PneuFab, enabled by FDM 3D-printed custom structures and temporal triggering methods. Then we implement and evaluate a design tool that allows users to play with parameters and preview the resulting forms until achieving their desired shapes. Showcasing design spaces including artifacts with complex geometries and tunable stiffness, we hope to expand access and dive into what more the digital blow molding fabrication can be.