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Understanding Fabric Performance Values for Internal Blinds

  • 18 August 2025

When you browse our fabric range for internal blinds, you’ll notice a set of technical values on certain fabrics, such as Ts, Rs, As, Tv, Rv, Av, and gtot.

These might look like a string of mysterious letters, but they’re actually very useful for choosing the right fabric for your space. They tell you how the fabric interacts with sunlight and heat, helping you balance natural light, glare control, and indoor temperature.

1. The Basics - How Light and Heat Behave

When sunlight hits your window blind, three things can happen:

  1. • Transmission - some energy passes through the fabric into the room.
  2. • Reflection - some energy bounces back away from the fabric.
  3. • Absorption - some energy is soaked up by the fabric, turning into heat.

These happen in both the visible light spectrum (daylight we see) and the wider solar light spectrum (which also includes invisible UV and near-infrared light).

2. The Symbols Explained

Solar properties (full spectrum: UV + visible + near-infrared)

  1. • TS | Solar Transmittion - % of total solar energy that passes through the fabric. Lower Ts means less heat enters.
  2. • RS | Solar Reflection - % of solar energy reflected away by the fabric. Higher Rs usually means better heat protection.
  3. • AS | Solar Absorption - % of solar energy absorbed by the fabric. Some of this absorbed heat may be re-radiated into the room.

Visible Light Properties (what our eyes see)

  1. • Tv | Visible Light Transmission - % of daylight that passes through. Low Tv = dimmer, good for glare control. High Tv = brighter, more daylight.
  2. • Rv | Visible Light Reflection - % of visible light reflected. Higher Rv can make interiors feel brighter and reduce glare.
  3. • Av | Visible Light Absorption - % of visible light absorbed by the fabric.

3. gtot - Total Solar Energy Transmittance

This value comes from EN 14501:2021 testing. It tells you how much of the sun’s total heat actually enters your room when the blind is down, factoring in both the fabric and the glazing.

That’s why you may see results for:

  1. • gtot C - tested with glazing type C (standard double glazing, low-e coating).
  2. • gtot D - tested with glazing type D (high-performance glazing with solar control coating).

Lower gtot = better heat control.

4. gtot Class Ratings in EN 14501

The standard converts gtot results into performance classes for summer comfort:

Class gtot value Performance description
Class 0 > 0.60 Very little heat control
Class 1 0.60 - 0.50 Modest heat control
Class 2 0.50 - 0.35 Moderate heat control
Class 3 0.35 - 0.15 Good heat control
Class 4 < 0.15 Excellent heat control

A Class 4 rating means only a small fraction of solar heat enters the room - ideal for keeping interiors cooler in summer.

5. Examples

To see how these values work in practice, here are three very different fabrics we sell - each with its own light and heat control characteristics.

That’s why you may see results for:

Fabric Ts (%) Rs (%) As (%) Gtot C Class Gtot D Class Tv (%) Rv (%) Av (%)
Quad 3% Soft Grey 10 51 39 0.4 1 0.26 2 7 57 36
Leicester BO Blanc 0 67 33 0.35 2 0.25 2 0 77 23
Fenchurch 3% Black 2 80 18 0.31 2 0.24 2 3 79 18

Quad 3% Soft Grey - Regular Screen Fabric

  1. • Heat Control: Moderate, with Class 1 (gtot C) and Class 2 (gtot D) ratings.
  2. • Light & Glare: Lets in 7% of visible daylight - enough for a softly lit interior while still reducing glare.
  3. • Reflection: Over half of the solar energy is reflected (51%), keeping the room cooler.

Leicester BO Blanc - White-Backed Blackout Fabric

  1. • Heat Control: Class 2 for both glazing types, blocking a significant amount of heat.
  2. • Light & Glare: 0% visible light transmission - complete blackout.
  3. • Reflection: High visible light reflection (77%) thanks to its white backing, which also boosts solar heat protection.

Fenchurch 3% Black - Unique Weave with Metallised Back

  1. • Heat Control: Class 2 for both glazing types, with outstanding reflection (80% solar, 79% visible).
  2. • Light & Glare: Only 3% of visible daylight gets through - superb for glare reduction.
  3. • Reflection: Like other darker screen fabrics, Fenchurch lets you enjoy daytime view-out, but its metallised back delivers reflection levels similar to a white-backed fabric. This means you get the best of both worlds - outward visibility and high heat rejection.

In short:

These values aren’t just technical jargon - they’re your guide to choosing a blind that delivers the right mix of comfort, daylight, and energy savings. Understanding them will help you get the look you want and the performance you need.

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