Intumescent glazing seals—often overlooked as mere accessories—are in fact the linchpin of fire-resistant glass systems. These specialized components transform passive glazing into active fire barriers by expanding up to 10× their original volume when exposed to heat, sealing critical gaps between glass edges and framing. This dynamic response is fundamental to containing flames, smoke, and toxic gases during building fires. Here, we examine their engineering principles, performance standards, and transformative impact on fire safety.