What Is Float Glass? The Foundation of the Glazing Industry
Almost every pane of glass you install — whether it's toughened, laminated, or part of an IGU — starts life as float glass. Understanding float glass helps you understand the entire product chain.
What Is Float Glass? Float glass is flat glass manufactured using the Pilkington float process, invented in the 1950s. Molten glass is poured onto a bath of molten tin and allowed to float and spread, producing a sheet with perfectly flat, parallel surfaces. The result is optically clear glass with consistent thickness and no distortion.
The Manufacturing Process 1. Raw materials (silica sand, soda ash, limestone, and recycled cullet) are melted in a furnace at around 1,550°C. 2. The molten glass flows onto the tin bath, where it spreads under gravity and controlled tension to achieve the desired thickness. 3. The glass ribbon moves through an annealing lehr — a long oven where the temperature is gradually reduced to relieve internal stress. 4. The cooled glass is cut into standard sheets (typically 3210mm × 2250mm or 6000mm × 3210mm) and inspected for defects.
Standard Thicknesses Float glass is manufactured in standard thicknesses from 2mm to 25mm, with 4mm, 5mm, 6mm, 8mm, 10mm, and 12mm being the most common in construction.
From Float to Finished Product Raw float glass (also called annealed glass) is relatively fragile compared to processed glass. In construction, it is almost always further processed before installation: • Toughened: Heat-treated to increase strength and change breakage pattern • Laminated: Two or more sheets bonded with a PVB interlayer • Coated: Low-E, tinted, or reflective coatings applied to one surface • Assembled into IGUs: Sealed with a spacer to form double or triple glazing
Annealed vs. Toughened In its raw float state, annealed glass breaks into large, sharp shards — a serious injury risk. This is why AS 1288 mandates toughened or laminated glass in most human impact zones. Annealed float glass is still used in low-risk applications like picture frames, interior partitions above 1.5m, and as the starting material for further processing.
Why Glass Weight Is Consistent Because float glass is manufactured to precise tolerances, its density is highly consistent at 2,500 kg/m³. This means the simple formula — 2.5 kg per m² per mm of thickness — works reliably across all float-based products. A 6mm toughened pane weighs the same as a 6mm annealed pane of the same area.