A U value, or overall heat transfer coefficient, quantifies heat loss in a building element like a wall, floor, or roof. It reflects the efficiency of heat transfer within different parts of a building. A higher U value implies poorer thermal performance in the building envelope, while a low U value typically suggests superior insulation. These values serve as a valuable means to predict how an entire building element behaves thermally, offering insight into the composite performance rather than relying solely on the properties of individual materials.
U values hold significance as they serve as the foundation for energy or carbon reduction standards. In practical terms, almost every external building component must adhere to thermal standards, typically defined by a maximum allowable U value.

Low emissivity (low-e or low thermal emissivity) pertains to a surface condition characterized by the emission of minimal levels of radiant thermal (heat) energy. While all materials inherently absorb, reflect, and emit radiant energy, the focus here is on a specific wavelength interval of radiant energy.

Emissivity is the value given to materials based on the ratio of heat emitted compared to a blackbody, on a scale from zero to one. A blackbody would have an emissivity of 1 and a perfect reflector would have a value of Zero .
Materials with low emissivity values tend to reflect more infrared radiation and absorb less heat.

Reflectivity and emissivity are inversely related properties, and their sum for an opaque material equals 1. For instance, in the case of a low-emissivity (low-e) material like aluminum foil, it exhibits a thermal emissivity value of 0.03 and a thermal reflectance value of 0.97. This indicates that the material reflects 97 percent of radiant thermal energy and emits only 3 percent. Low-emissivity building materials encompass window glass with metal-oxide coatings, housewrap materials, reflective thermal insulations, and other types of radiant thermal barriers.

The thermal resistance, often denoted by the letter "R," is a measure of a material's ability to resist the flow of heat. The higher the thermal resistance (R-value), the better the material is at impeding heat transfer. It is commonly used in the context of building insulation to evaluate how effectively a material or assembly resists heat flow.
The R-value is calculated by dividing the thickness of the material by its thermal conductivity.
In the context of building construction, a higher R-value is desirable, indicating better insulation and reduced heat transfer through walls, floors, roofs, or other building elements. It helps in assessing the overall thermal performance and energy efficiency of a structure.

Thermal conductivity is a material property that describes how well a substance conducts heat. It is a measure of the ability of a material to transfer heat through its mass. The higher the thermal conductivity, the more effective the material is at conducting heat.

Improved performance is achieved with multiple layers of the product and airspaces between them. If the product is merely "doubled" without any airspace between the layers, the benefit is minimal.

Regarding R-values for Reflective Insulation and the reasons for their variation in different applications: Reflective insulation R-values depend on two primary criteria:

1. Heat flow direction.
2. The quantity of air space within a closed cavity on the reflective side of the product in a building assembly.

This variation in R-values for different applications is attributed to the differences in air space amounts and heat flow directions in each scenario.

To maximize the effectiveness of either reflective insulation or a radiant barrier, it is necessary to have a minimum thickness of air space on the reflective side. The benefits of reflective insulation stem from the interaction between the highly reflective surface and this air space. When the reflective surface is in direct contact with other building materials, it can conduct energy. An air space, specified on one or both sides (always on the reflective side), helps prevent this and is crucial for achieving the stated R-value, especially in enclosed spaces when instructed.

Yes! Xcel Insulation is a highly versatile product and can be used in combination with all other forms of insulation. By adding Xcel Insulation to an existing insulation, you are ensuring you have a high performance insulation which will save you money on your energy bills.

Simply send us an email at sales@xcelinsulation.com and we can discuss your requirements direct for a great price.