R factor

Definition

The R factor, or R-value, measures the thermal resistance of a material. It quantifies how well a material can resist the flow of heat.

5 Must Know Facts For Your Next Test

1. R-value is directly proportional to thermal resistance: higher R-values indicate better insulation.
2. The unit of R-value in the metric system is $\text{K} \cdot \text{m}^2 / \text{W}$.
3. R-values are additive for layers of materials; total R-value is the sum of each layer's R-value.
4. Typical materials with high R-values include fiberglass, foam board, and cellulose.
5. R-value depends on thickness and type of material, making it essential for determining energy efficiency in buildings.

Review Questions

• What does a higher R-value indicate about a material's thermal resistance?
• How do you calculate the total R-value for multiple layers of different materials?
• Why is the R-value important in evaluating building insulation?

Related terms

Thermal Conductivity:

A measure of a material's ability to conduct heat, commonly represented by $k$ or $\lambda$. Lower thermal conductivity means better insulating properties.

U-Value: The overall heat transfer coefficient, representing how well a building element conducts heat. It is the inverse of the total R-value.

Heat Transfer: The movement of thermal energy from one object or material to another via conduction, convection, or radiation.