Insulating units consisting of two panels of glass sealed around the edges by an airtight joint and separated by a layer of air, other gases or a vacuum (excl. coloured throughout the mass, opacified, flashed or having an absorbent or reflective layer)
Multiplewalled insulating glass consisting of two panels of glass with an interlayer of glass fibre, and multiplewalled insulating glass consisting of three or more panels of glass (excl. coloured throughout the mass, opacified, flashed or having an absorbent or reflective layer)