German term (edited): U-Werte: 0,46 / 0,46 / 0,46 W/mІK

U-value => Wärmedurchgangszahl f, spezifischer Wärmefluss m, Wärmeübergangszahl f

http://www.doityourself.com/stry/uvalue
If you've ever been shopping for a window, you've no doubt encountered a term that you're probably not all that familiar with - U-value. U-values are a rating of energy efficiency, and they are used to rate and compare windows, exterior doors, skylights and certain other exterior building components, including exterior walls. U-values are also the standard used in the building codes for specifying the minimum energy efficiency values for all of these components.
Most people are much more familiar with R-values, which are used to rate how well a material such as insulation resists the flow of heat through it. The higher an R-value is, the more heat loss it resists, and therefore the more energy efficient it is. U-values differ from R-values in two important ways, and when you're shopping for energy-efficient components for your house, it helps to understand the difference.
First of all, where the R-value is used to rate the energy efficiency of a single component - a batt of insulation for example - U-values rate the energy efficiency of the combined materials in a building component or section. For example, in a typical insulated window you have the two panes of glass, the dead air between the glass, the frame material and perhaps some weatherstripping or sealants that hold everything together. Because each of these components works together as a unit, the U-value is used to indicate the energy efficiency of this entire assembly.
The second distinction is that U-values rate how much heat is conducted through this combination of materials. So, where R-values rate how much heat loss the material resists from passing through it, U-values rate how much the heat the component allows to pass through it. Therefore, while a high R-value indicates good energy efficiency - R-19 is better than R-11, for example - while a low U-value indicates good energy efficiency - U-0.35 would be better than U-0.43.

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Note added at 14 mins (2006-09-29 11:00:01 GMT)
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http://en.wikipedia.org/wiki/Thermal_transmittance
Thermal transmittance
Thermal transmittance, also known as U-value, is the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure. It is expressed in watts per square metre per kelvin, or W/m2K.
Well-insulated parts of a building have a low thermal transmittance whereas poorly-insulated parts of a building have a high thermal transmittance.
Heat transfer = area × (thermal transmittance) × (difference in temperature)