Mold bridging occurs when the sheet spans across a recess or between features instead of entering the intended geometry. The material forms a tent-like surface and may seal before air can be evacuated from the space below.
A sheet that is too cold can resist bending into the recess. Closely spaced features, insufficient pre-stretch, poor venting, and early contact at surrounding high points can create the same result. Bridging can therefore be both a thermal and geometric defect.
Correction
The unsupported span and first-contact points should be examined. Local venting must remain open after the surrounding sheet touches the tool. Downholders, plug assist, or directed pre-stretch can subdivide the span and guide material into the recess.
Heat should be adjusted only after the airflow path is confirmed. Excessive softening may pull the bridge down but create webbing or severe thinning between features. Persistent bridging tied to fixed geometry usually requires a tool or process-aid change rather than a global recipe adjustment.