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Thermal break

Also called thermal barrier

A strip of insulating material that separates the inside and outside halves of a metal frame.

Metal conducts heat, so a metal frame is made in two halves, one facing out and one facing in, joined only by a material that conducts poorly. Heat has no metal path from one side to the other.

The break is either a pair of rigid plastic struts crimped into both halves, or a channel poured full of resin, after which the metal bridging it is cut away.

Bottom rail of a thermally broken aluminum sash in section, outside at left

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Aluminum sash, bottom rail in section

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