What is the value of w?

The lambda (λ) value, or the Thermal conductivity, or 'k-value' of a material, is a value that indicates how well a material conducts heat. It indicates the quantity of heat (W), which is conducted through 1 m² wall, in a thickness of 1 m, when the difference in temperature between the opposite surfaces of this wall equals 1 K (or 1 ºC).

Explanation:

I copied from google. I do not think this is what you need. But give it a go.

The lambda (λ) value, or the Thermal conductivity, or 'k-value' of a material, is a value that indicates how well a material conducts heat. It indicates the quantity of heat (W), which is conducted through 1 m² wall, in a thickness of 1 m, when the difference in temperature between the opposite surfaces of this wall equals 1 K (or 1 ºC).