Realizing precise therapy for glioblastomas (GBMs), a kind of high-frequency malignant brain tumor, is of great importance in improving the overall survival (OS) of patients. With relentless efforts made in the past few years, a sponge medium has been introduced into concurrent tumor treating fields (TTFields) and radiotherapy to enhance therapy efficacy for GBMs, and some progresses have been witnessed. However, the specific physical and chemical characteristics of the sponge that can be used for GBMs have not been reported as far as we know. Therefore, this study aims to develop a simple yet robust method to select a candidate sponge medium and verify its safety in advanced concurrent TTFields and radiotherapy for GBMs through interdisciplinary investigation among materials science, medical physics, and clinical radiation oncology. Significantly, latex-free polyurethane (PU) sponges with a Hounsfield unit (HU) value lower than -750, which exhibit almost no negative influence on planning computed tomography (CT) imaging and radiotherapy dosimetry, are demonstrated to be available for concurrent TTFields and radiotherapy for GBMs. Moreover, in clinical research, the achieved clear CT images, negligible scalp toxicity, lower residual positioning errors, and high compliant rate of 82% over the selected representative sponge sample corroborate the availability and safety of PU sponges in practical applications for GBM treatment.