Deformable thermal protection structures play a pivotal role in morphing vehicles’ high‑speed performance by mediating the trade‑off between thermal resistance and structural flexibility. Internal spatial architectures are essential to cooling schemes for efficient coolant transport and augmented heat transfer, while they nevertheless introduce localized stress concentrations that significantly degrade structural fatigue life in applications demanding large, repeated deformations, like morphing plane wings. We use Finite Element (FE) analysis here to evaluate how the mechanical performance is influenced by the internal rim curvature under near‑realistic loading conditions, providing insights for the design of deformable thermal protection structures. Quantitative analysis shows that selecting the right fillet radius can reduce stress-concentration factors by up to 9.8% under combined thermo-mechanical loading. Smaller-diameter channels exhibit greater sensitivity to these curvature adjustments. Optimized rim curvature offers clear engineering benefits for casting large rubber morphing skins. Controlled fillets help prevent demolding damage and improve fatigue resistance, enabling more durable adaptive thermal protection in high-temperature applications.