Window shades play an important role in building performance. To maximize performance, it’s important to choose the right shading system for the job. That means considering shade fabric characteristics including color, weave, openness factor, and more.

To help make this choice easier top fabric weavers like Mermet® USA and Phifer provide charts of technical measurements outlining the thermal and optical performance of each color and openness combination. Thermal properties relate to heat control, while optical properties relate to visual aesthetics. Performance is measured at a 90° angle to the fabric surface.

Here are the performance specifications you will typically find on shade fabric swatch cards, and what they mean:

Solar Ref Out / (Rs) (Total Solar Reflectance)
This is the percentage of solar energy directly reflected by the fabric. The higher this number is, the more heat the fabric reflects. The percentages of Rs, As, and Ts should add up to 100.

An example from the Mermet USA E Screen swatch card.

As (Total Solar Absorptance)
The percentage of solar energy absorbed by the shade fabric. The lower the number, the cooler it is near the window. This number will always be opposite of Rs: If the Rs number is high, As will be low, and vice-versa.

Solar Trans / Ts (Total Solar Transmittance)
The percentage of solar energy directly transmitted through the fabric. The higher the number, the more solar energy is being allowed through into the building.

Light Ref / Rv (Reflectance in the Visible Spectrum)
The percentage of visible light reflected by the fabric. Lighter colors will have a higher number, meaning they reflect more light and reduce glare.

Light Trans / Tv (Transmittance in the Visible Spectrum)
The percentage of visible light directly transmitted through the fabric. This includes both direct and diffused light. Darker colors will have a smaller number. They allow more visible light through, which is why darker colors have better view-through characteristics.

Thermal and optical properties of Phifer Performance Plus.

Rs IR (Reflectance in the Infrared Spectrum)
The percentage of solar energy in the infrared range reflected by the fabric. The IR spectrum is where heat is generated, so the higher the number, the cooler the surface of the shade fabric will be.

UV Transmittance
The percentage of ultraviolet (UV) energy directly transmitted through the fabric. A higher number means more UV light getting through. In the long term, this can lead to fading of fabric covered furnishings.

Color Rendition Index
This percentage represents a shade fabric’s impact on the color spectrum. A high percentage means the shade fabric is having less impact on the natural light spectrum.

Solar Heat Gain Coefficient (SHGC)
The percentage of solar energy that reaches a building ‘s interior. This takes into account shading and glazing systems. A low number indicates less solar heat is being transmitted.

Draper® provides fabric swatch cards with this information on every fabric offered on FlexShade® window shades. You can find them under the “Technical Documents” tab on each fabric page. To research our offerings and compare the numbers, click here.