Fiberglass fabric thermal shrinkage is the primary cause of PTFE tape dimensional instability. At PTFE sintering temperatures (360-400°C), residual weaving stress is released. If unrestrained, fabric shrinks; if restrained, latent stress is locked in, causing later shrinkage during adhesive curing (150-200°C) and end-use heating. Solution: use pre-heat-set fiberglass with <0.5% shrinkage at 400°C, eliminating residual stress before coating.