The general characteristic value for thermal conductivity of basic soda lime silicate glass is 1 W/(m.K)

This value, for normal annealed glass without any further toughening, is not a precise requirement with which the glass shall strictly comply, but is the generally accepted figures for use in calculations where a high degree of accuracy is not required.

[Reference: BS EN 572-1: Glass in building — Basic soda lime silicate glass products - Part 1: Definitions and general physical and mechanical properties]