<p>Headforms are commonly used as tools in the design and qualification of personal protective equipment. Deformable headforms, containing elastomeric brain models, provide a unique opportunity to directly measure the <i>in situ</i> intracranial strain from an impact; however, these physical models require significant refinement to ensure biofidelity. In the present work, the response and biofidelity of a deformable headform and brain model were investigated, comparing the influence of different boundary conditions on its response. More precisely, the presence or absence of a tentorium or a brainstem model were investigated, focusing on the resulting intracranial displacement and strain fields. The headforms were subjected to a series of linear impacts and deformations within the brain were tracked using embedded radiopaque markers and high-speed X-ray imaging. X-Ray Digital Image Correlation was used to calculate displacement and strain fields within the headform. The biofidelity of the displacement and strain fields within the headform design having both a tentorium and a brainstem were compared to Post-Mortem Human Subject (PMHS) data under identical impact conditions. The biofidelity was ranked using a CORA analysis to provide insight for future design refinements of the headform. The biofidelity ratings for displacement were highest in the frontal and occipital regions (good-excellent) and were worst in the insular region (marginal). Meanwhile, the strain biofidelity rating was best in the frontal (good) and cerebellum (good) regions and worst in the insular region (poor-marginal). This work addresses previous limitations in enhancing the biofidelity of closed headforms and offers opportunities for further improvement through the comparison to PMHS data.</p>