When a partner orders a screen roller blind or a ZIP system, the specification often just says “screen, grey”. Yet the missing figure — the openness factor — decides whether the user will see the garden through the blind, whether an office screen will still be readable at three in the afternoon, and how much heat will get into the room.
This guide is written for specifiers, contractors and interior decorating businesses. It explains what the openness percentage actually measures, how fabric colour changes the result, and how to write exactly what the building needs into your enquiry.
What the openness factor is
Screen fabric is woven from coated yarns, with small, regular openings between the threads. The openness factor (OF) is the percentage of the fabric surface taken up by those openings. A 3 % fabric has, put simply, 3 cm² of openings for every 100 cm² of surface.
- Lower percentage (1 %) — a denser weave, less direct light and glare, a weaker view out.
- Medium percentage (3 %) — the compromise most often chosen for workspaces.
- Higher percentage (5 % and above) — more view and daylight, but also more sun passing straight through the openings.
Important: screen is not blackout. Even a 1 % fabric does not make a room dark — it filters light. For bedrooms, hotel rooms or projection rooms, choose a blackout fabric or a combination of two layers.
1, 3 and 5 % compared
On paper the differences between these values look small, but on the window they are clearly visible. The table shows where each value is most often used:
| Openness | View out | Glare control | Typical use |
|---|---|---|---|
| 1 % | Weaker, outlines visible | Best | Offices with screens on the west side, receptions and meeting rooms in strong sun |
| 3 % | Good | Good | Offices, classrooms, commercial space — the most common choice |
| 5 % | Very good | Moderate | Apartments, living rooms, restaurants, spaces where the view matters |
| 10 % | Almost unobstructed | Weak | Spaces with little direct sun, where the fabric is for daytime privacy and appearance |
For most commercial buildings, 3 % is the starting point. You move away from it when there is a clear reason: lower when glare is the problem, higher when the view matters more than protection.
Colour changes the result as much as the percentage
Two fabrics with the same openness factor can behave completely differently simply because one is white and the other anthracite. Colour affects two things that pull in opposite directions — view and heat:
Dark colours — anthracite, black, dark grey
A better view out and less glare, because a dark surface does not “glow” in the sun and the eye sees the outside scene through it more easily. On the inside of the glass they absorb more heat, so the fabrics themselves get warmer.
Light colours — white, beige, light grey
They reflect more solar energy, so they are better when heat is the main problem, especially on external systems. But in direct sun the fabric glows: the view out is weaker and contrast on screens is poorer.
Mid tones — grey, sand
A compromise for buildings where no single requirement dominates, and for façades where the architect wants an even, calm appearance from outside.
Inside or outside — same fabric, different job
The openness factor is chosen differently depending on where the fabric sits relative to the glass:
- Internal screen roller blind. The heat has already passed through the glass, so the main task is controlling glare and the view. Here the choice of percentage and colour is above all a question of visual comfort.
- External ZIP system. The fabric stops the sun before the glass, so a somewhat higher openness can be allowed without overheating. A darker 3–5 % fabric outside often gives a better view than a dense light fabric inside — and protects better against heat.
That is why the position must always be stated in the specification. “Screen 3 %, anthracite, external ZIP” and “screen 3 %, anthracite, internal roller” are not the same product and do not give the same result.
How to choose: three questions for each group of positions
Before you write down a percentage, answer three questions. The answers may differ from floor to floor and from façade to façade:
- What is the main problem? Glare on screens — 1 to 3 %. Heat — an external system, with the percentage chosen for the view. Daytime privacy — 3 to 5 %, in a lighter tone.
- How important is the view? If large glazing is the very reason the building was designed that way, choose a darker colour and 5 %, not a denser weave.
- What happens in the evening? Screen does not give privacy at night: when the lights are on inside and it is dark outside, the interior is visible through the fabric. If that is a problem, a second layer is needed.
The third point is the most common reason end users are dissatisfied — and it is not a fabric defect, it is simply how screen works. It is better for the client to hear it from the specifier in advance than to discover it on the first evening.
Screen fabric samples for your project
We work exclusively with businesses — specifiers, contractors and interior decorating businesses. Send us your measurement list with the use and orientation of each room and receive a proposal for openness and colour, together with fabric samples.
Send an enquiry →What to put in your enquiry
To prepare an accurate quotation and the right samples, add the following to the measurement list for each group of positions:
- System type and position — internal roller or external ZIP.
- Required openness factor — or just the main problem (glare, heat, view), and we will suggest a value.
- Colour or tone — and whether the architect wants a uniform façade appearance from outside.
- Room use and orientation — a west-facing office and a north-facing living room do not get the same fabric.
We send screen fabric samples in several openness values and colours to partners free of charge. Look at them on the actual window, in sunlight: the difference between 1 % and 5 % is barely visible on a monitor, but obvious on the glass.
Frequently asked questions
What does the openness factor of a screen fabric mean?
It is the percentage of the fabric surface taken up by the openings between the threads. A 3 % fabric has about 3 % open area. The lower the percentage, the better the fabric controls glare, but the weaker the view out.
Which openness is best for an office?
For most offices, 3 %. If the room faces west or has many screens facing the window, 1 % is chosen. A darker colour further reduces glare and preserves the view out.
Does a 1 % screen fabric darken the room?
No. Screen filters light but does not create darkness. Bedrooms, hotel rooms and projection rooms need a blackout fabric or a combination of two layers.
Can you see inside through a screen blind at night?
Yes, when the lights are on inside and it is dark outside. Screen protects privacy during the day. For privacy at night a second layer or a different type of fabric is needed.
Which screen fabric colour is better, light or dark?
Dark gives a better view and less glare; light reflects more heat. For internal systems in offices a darker or grey fabric is usually chosen, while for external systems the decision depends on whether the priority is the view or heat.
Conclusion
The openness factor is just one number, but it determines how the user experiences the space: whether they can see out, whether their screen is glaring and whether they are too warm. Together with fabric colour and position, these are the three details that belong in every specification.
For most commercial spaces the starting point is 3 %, in a darker tone. Move away from it deliberately — lower for glare, higher for the view — and the blind will do exactly what is expected of it.