Fabric Openness Factor Guide: How to Choose 1%, 3%, 5% or 10% for Your Project (2026)

Openness factor is the single number that determines how much light, heat, and visibility pass through a roller blind fabric. Yet most procurement specifications still treat it as an afterthought — copying “3% openness” from a previous project without asking whether the building orientation, room function, or motor system demands a different choice.

This guide breaks down what openness factor actually measures, how each level (1%, 3%, 5%, and 10%) performs in real commercial environments, and which one to write into your next specification.

The short answer

Openness factor is the percentage of a fabric’s surface area that is open space between yarns. A 3% openness fabric has 3% open area and 97% closed area. The lower the number, the more light and heat are blocked; the higher the number, the more view-through and daylight you retain.

For most commercial roller blind projects:

• 1% openness — maximum glare control, minimal view-through. West facades, conference rooms, cinemas.
• 3% openness — the default for offices and hotels. Balanced glare reduction with usable outward visibility.
• 5% openness — view preservation priority. Lobbies, retail showrooms, residential living areas.
• 10% openness — maximum daylight and view. Light-filtering applications, decorative screens, interior partitions.

What openness factor actually measures

Openness factor (sometimes called “openness ratio” or “open area”) is measured by shining light through the fabric and calculating what percentage passes through the gaps in the weave. It is a physical property of the textile construction, not a coating property.

Three variables control openness:

Yarn diameter

Thicker yarns close more surface area. A 1% openness fabric typically uses heavier denier yarns than a 5% fabric in the same product family.

Weave density

More picks per centimeter (horizontal yarns) and more ends per centimeter (vertical yarns) reduce the gaps. Tighter weaves produce lower openness but add weight and stiffness.

Yarn shape

Round yarns leave predictable, uniform gaps. Flat or ribbon-shaped yarns can be packed tighter, achieving lower openness at the same weight. Some premium sunscreen fabrics use flat yarns to hit 1% openness without the weight penalty of thick round yarns.

A common misconception: openness factor is not the same as visible light transmittance (Tv). A 3% openness fabric does not transmit exactly 3% of visible light. Tv is typically lower than the openness number because yarns scatter and absorb light that strikes them at angles. Always request a tested Tv value from the supplier, not just the nominal openness percentage.

1% Openness: Maximum solar control

A 1% openness fabric blocks roughly 99% of direct solar radiation from passing through the weave. It is the tightest construction commonly available in roller blind sunscreen fabric, and it is specified when glare is the primary problem.

Where it belongs

• West- and south-facing facades in hot climates (Middle East, Southern US, Southeast Asia) where afternoon sun creates unbearable glare and heat gain.
• Conference rooms and video-call studios where screen washout from window glare is a functional failure.
• Cinemas, auditoriums, and projection rooms that need near-blackout conditions while maintaining some air permeability.
• Museums and galleries where UV and visible light damage exhibits but some filtered daylight is acceptable.

Trade-offs

At 1% openness, outward visibility is severely reduced. Occupants can barely see through the fabric, which can create a “closed-in” feeling in occupied spaces. For hotel guest rooms and open-plan offices where view-through matters, 1% is usually too restrictive unless paired with a dual-roller system (sunscreen + blackout on separate tubes).

Weight is also higher — typical 1% sunscreen fabrics run 420–520 GSM, which increases the load on the roller mechanism and may require a larger tube diameter or a stronger motor.

3% Openness: The commercial default

3% is the most-specified openness factor in commercial roller blinds worldwide, and for good reason: it sits in the performance sweet spot between solar control and visual comfort.

Where it belongs

• Hotel guest rooms — typically paired with a separate blackout roller for night use. The 3% sunscreen provides daytime privacy and heat rejection while preserving enough view-through for guests to orient themselves.
• Office buildings — 3% cuts glare on monitors and work surfaces without turning the space into a bunker. Most green building standards (LEED, BREEAM, WELL) accept 3% sunscreen as a glare-control strategy.
• Schools and universities — classrooms benefit from reduced glare on whiteboards and screens while maintaining daylight for student alertness.
• Healthcare facilities — patient rooms and corridors where diffused natural light supports recovery but direct sun must be controlled.

Why specifiers default to 3%

When you are unsure which openness to specify, 3% is the lowest-risk choice. It performs acceptably on most orientations, satisfies most energy codes, and is the openness level that fabric manufacturers keep in the deepest inventory. Lead times on 3% fabrics are typically 2–4 weeks shorter than on 1% or 10% specialties.

5% Openness: View-first applications

At 5% openness, outward visibility becomes the primary design benefit. The fabric still blocks 95% of direct solar radiation, but the larger gaps in the weave let occupants see the landscape, cityscape, or courtyard outside with reasonable clarity.

Where it belongs

• Hotel lobbies and restaurants — where the view is part of the guest experience. A waterfront lobby or mountain-view restaurant sacrifices nothing functionally by going to 5%.
• Retail showrooms — visual connection to the street draws foot traffic inward. Car dealerships, fashion retail, and flagship stores all benefit.
• Residential living rooms and penthouses — homeowners almost always prefer more view-through. 5% sunscreen on roller blinds is increasingly specified in high-rise apartments as the daytime window treatment.
• Airport lounges and transit hubs — large glass facades where full view preservation reduces the “underground” feeling.

Trade-offs

On unshaded west facades in hot climates, 5% openness may not cut enough solar heat gain. In those cases, specifiers should either add an external shading device (louver, overhang) or drop to 3% on the affected elevations while keeping 5% on north- and east-facing glass.

10% Openness: Light-filtering and decorative

10% openness fabrics are a different category. They are not primarily solar-control products — they are light-filtering and decorative textiles that happen to provide some UV reduction.

Where it belongs

• Interior partitions and room dividers — where the goal is visual separation without full opacity.
• Decorative roller blinds in residential settings where privacy at night is handled by curtains or shutters, and the daytime blind is purely for light diffusion.
• Outdoor pergola sides and patio screens — where airflow is as important as shade. Outdoor shade fabrics in 10% openness are commonly specified for zip-screen systems.
• Skylights and atrium screens — overhead applications where some diffused daylight is desired but direct sun must be softened.

Trade-offs

10% openness provides minimal glare reduction on work surfaces. It should never be specified as the primary glare-control fabric in an office or classroom. Its role is supplementary — filtering and softening light, not blocking it.

Side-by-side comparison

Five questions that decide your openness factor

Work through these in order. The answer to each one narrows your range.

1. What is the room function?
Conference room, cinema, or projection space → start at 1%. Office, classroom, or hotel guest room → start at 3%. Lobby, retail, or residential living → start at 5%. Decorative or partition → start at 10%.

2. Which direction do the windows face?
West- and south-facing glass in low-latitude climates receives the most intense solar load. If you started at 3%, consider dropping to 1% on those elevations. North- and east-facing glass is less demanding — you can often move up one level (3% → 5%) without penalty.

3. Is there external shading?
If the building already has louvers, overhangs, or adjacent structures that shade the glass for part of the day, the fabric does less work. You can safely specify a higher openness factor. If the glass is fully exposed, stay at the lower end.

4. How important is the view?
In hospitality, the view is a revenue driver — a room overlooking the ocean or skyline commands a premium. Do not sacrifice view-through for marginal solar gain. In these cases, 5% with external shading outperforms 1% with no view.

5. Will the blinds be motorized?
Heavier fabrics (1% openness, higher GSM) require more torque from the motor. If you are specifying motorized roller blinds, check the motor’s weight capacity against the fabric weight × blind area. This is especially relevant for large-format blinds over 2.5 meters wide. See the motorization section below.

Openness factor and motorized roller blinds

The relationship between openness factor and motorization is often overlooked in specifications, but it directly affects cost, reliability, and system compatibility.

Weight and torque

Lower openness fabrics are heavier because they use thicker yarns and tighter weaves. A 1% openness fabric at 480 GSM on a 3-meter-wide blind creates a fabric load of approximately 1.4 kg/m² × the blind area. A 5% openness fabric at 340 GSM on the same blind is roughly 30% lighter. The motor must be sized for the heavier fabric, or the blind width must be limited.

Motor compatibility

Not all roller blind motors handle the same weight range. Somfy and Dooya — the two most common motor brands in hospitality projects — publish maximum load ratings per tube diameter. A 35mm tube motor typically handles up to 3–4 Nm of torque, which is sufficient for most 3% and 5% fabrics on blinds up to 2.5 meters wide. For 1% fabrics on wider blinds, a 45mm tube with a 6–8 Nm motor is often required.

To eliminate this guesswork, motorized-ready fabric series are pre-tested against specific motor systems. The fabric weight, stiffness, and winding behavior are validated for Somfy and Dooya motors, so specifiers can select an openness level knowing it will work with the automation hardware already in the project budget.

Winding behavior

Tighter-weave fabrics (1%, 3%) roll more cleanly onto the tube because the fabric is stiffer and tracks straighter. More open fabrics (5%, 10%) can be more flexible and may require edge guides or a larger tube diameter to prevent telescoping — where the fabric layers shift to one side over repeated cycles. This is a common cause of motor strain and premature failure in automated systems.

Technical checklist for your specification

When writing openness factor into a procurement specification, include the following data points — not just the nominal percentage:

1. Tested openness factor — per ISO 9050 or manufacturer test report. Do not accept a “nominal” value without a test certificate.
2. Visible light transmittance (Tv) — measured per EN 410 or NFRC 200. This is the number your lighting designer actually needs.
3. Solar heat gain coefficient (SHGC) — the total solar energy entering through the fabric + glass system. Required for energy modeling.
4. UV transmittance (Tuv) — critical for museums, galleries, and healthcare. Should be below 5% for most commercial applications.
5. Fabric weight (GSM) — drives motor sizing and tube diameter.
6. Fire rating — NFPA 701, BS 5867 Part 2, DIN 4102 B1, or local equivalent. Openness factor does not affect fire performance, but both must be specified together.
7. Dimensional stability — per ISO 11502. Tighter weaves (lower openness) can be more prone to thermal shrinkage in extreme heat. Confirm stability data for the climate zone.

Dual-roller systems: combining openness levels

In hotel guest rooms and premium offices, the most common specification is a dual-roller system: one tube with a 3% or 5% sunscreen for daytime use, and a second tube with a 0% blackout fabric for night and presentation mode.

This approach gives occupants the best of both worlds — view-through and glare control during the day, total darkness at night — without forcing a compromise on either. The openness factor choice for the sunscreen roller can then be optimized purely for daytime conditions.

When specifying dual rollers, confirm that the headbox or bracket system accommodates two tubes and that the motorization system supports independent control of each. Most modern motor systems (Somfy RTS, Somfy io-homecontrol, Dooya DM) handle dual-motor configurations through a single controller.

Openness factor and sustainability credits

Openness factor contributes to several green building rating criteria:

• LEED v4.1 EQ Credit: Daylight — specifies maximum glare thresholds. Lower openness fabrics help achieve compliance on west facades.
• WELL Building Standard: Light Feature 02 — requires glare control strategies. Documented openness factor + Tv values satisfy the prescriptive path.
• BREEAM HEA 01: Visual Comfort — includes glare control requirements. 3% sunscreen is the standard reference specification.
• Energy codes (ASHRAE 90.1, IECC) — solar heat gain through fenestration is modeled with SHGC values. Lower openness fabrics contribute to lower whole-building SHGC, reducing cooling load calculations.

If your project is pursuing any of these certifications, request a product-specific EPD (Environmental Product Declaration) or HPD (Health Product Declaration) from your fabric supplier. These documents, combined with tested Tv and SHGC data, streamline the credit documentation process.

Frequently asked questions

Can I mix different openness factors on the same building?

Yes, and you should. A common best practice is to specify 1% on west and south facades, 3% on east facades, and 5% on north facades or where the view is a priority. Many projects also use different openness levels on different floors — lower openness on exposed upper floors, higher openness on lower floors shaded by adjacent buildings or landscaping.

Does fabric color affect openness performance?

Openness factor is a geometric measurement — it measures the physical gaps in the weave, not the color. However, darker colors absorb more solar energy (higher solar absorptance), which means the fabric itself gets hotter. On a south-facing facade in a hot climate, a dark-colored 3% fabric may transfer more heat to the interior through convection than a light-colored 3% fabric. Always request the solar absorptance value alongside openness when comparing color options.

What is the difference between openness factor and shade coefficient?

Shade coefficient (SC) is an older metric that compares the solar heat gain through a treated window to an untreated clear window. It has been largely replaced by SHGC (Solar Heat Gain Coefficient) in modern standards. Openness factor is a property of the fabric alone; SC and SHGC are properties of the fabric + glass system. You need both: openness to select the fabric, SHGC to model the building energy performance.

How do I verify the openness factor of fabric I have already received?

The simplest field test is to hold a known light source behind the fabric and measure the lux on each side with a light meter. The ratio (transmitted ÷ incident) approximates Tv, which is correlated with but not identical to openness. For a precise measurement, request a lab test per ISO 9050 from an independent testing facility.

Is lower openness always better for energy savings?

Not necessarily. In cold climates, solar heat gain through windows reduces heating load. A 5% openness fabric on south-facing glass in a northern climate can passively heat the building during winter, reducing energy consumption. Lower openness (1%) is better for cooling-dominated climates; higher openness (5%) can be beneficial in heating-dominated climates when combined with appropriate glazing.

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