A thin, flexible material used in guided bone regeneration (GBR) to locally augment deficient sites in implant patients. By creating a secluded space, the barrier prevents epithelial cells and fibroblasts from proliferating into the augmentation site, whereas the slower-growing angiogenic and osteogenic cells have exclusive access to the membrane-protected space. The first membranes were made of bioinert expanded polytetrafluoroethylene (e‐PTFE), which is nonresorbable and therefore required removal with a second surgical procedure. Bioresorbable membranes, either of synthetic polymers or of animal‐derived collagen, are often preferred in daily practice. Although their barrier function is limited in time, they do not require a second surgical procedure for membrane removal. Barrier membranes exclude undesirable cell types from entering the secluded area of the bony or periodontal defect during healing. Membrane configurations are designed for specific applications and vary in shape, size, and thickness. See: Guided bone regeneration (GBR); Guided tissue regeneration (GTR); Collagen membrane; Expanded polytetrafluoroethylene (e‐PTFE) membrane.