Joints in sex dolls are engineered to balance realism, strength, and durability. Most commonly, manufacturers use a combination of ball-and-socket, hinge, and silicone- or elastomer-based connections to mimic human range of motion. The ball-and-socket joint provides multi-directional movement, especially in shoulders and hips, allowing for natural posing and fluid rotation. Hinges are often used in elbows, knees, and fingers to deliver stable bending angles while maintaining a compact form factor. The choice of materials for joints is critical: softer elastomer cores can absorb impact and reduce squeaks, while hard shells offer long-term stability.
Mobility is enhanced by thoughtful engineering of the limb-socket interfaces. Tolerances are calibrated to allow smooth articulation without looseness that can degrade pose fidelity over time. Locking mechanisms or quick-release features may be included to adjust stiffness or to facilitate precise posing. Internal reinforcement, such as ribbing or layered composites, helps distribute stress during movement, reducing wear at high-stress points. Lubrication systems, when used, must be skin-safe and non-staining. The science also considers heat and weight distribution; heavier dolls require stronger joints and sometimes internal supports to maintain pose without sagging. Understanding these principles helps buyers choose models that hold poses reliably and age well with repeated use.