Wiktionary

1. k-value(Noun)

   thermal conductivity; the time of rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient. In English (inch-pound) units of measurement; it is the number of BTUs that pass through a 1 inch thickness of a square foot sample of material in 1 hour with a temperature difference between the two sufraces of 1 degree F.