How solar shade fabric works.

Openness factor

The single number that decides how much you see through a shade, how much glare gets past it, and how much privacy it gives you after dark.

Openness factor is the percentage of a shade fabric made up of holes rather than yarn. A 5% openness fabric is 5% air. It is the first number to settle on, because it governs view-through, glare control and privacy simultaneously — and those three pull against each other.

Lower openness means less glare and more privacy, and less of the view. Higher openness means you keep the view and lose control of the glare. There is no fabric that gives you all three; choosing openness is choosing which one matters most in that room.

Openness is also not the same as darkness. A dark 3% fabric and a white 3% fabric have the same holes and behave very differently — see the note on colour below.

0% — blackout

No holes. Complete light blockage. No view-through at all. Specified where darkness is the requirement: screening rooms, bedrooms, imaging suites.

1–3%

Strong glare control and good night-time privacy, with a soft, restricted view. The usual choice for west and south exposures with a screen-based workforce.

5%

The commercial default. Meaningful glare reduction while keeping a usable view. Where a project standardises on one fabric, it is usually this.

10%+

View-first. Keeps the outlook nearly intact and reduces heat more than glare. Best on north exposures, atria and lobbies where the view is the point.

Weave

Two fabrics at the same openness can look and perform differently. The weave is why.

Openness tells you how much of the fabric is air. Weave tells you how that air is arranged — and the arrangement changes what you actually see through it.

A basket weave puts the openings in even squares, which gives the cleanest view at a given openness. A twill offsets each row, producing a diagonal wale that reads differently from the room side than the street side. A satin weave is deliberately two-faced: white to the street for heat rejection, a different colour to the room.

The seven weave definitions IWS publishes are on the fenestration reference, alongside the fenestration values they affect.

Colour, view and heat

Dark fabric gives the best view and the worst heat performance — unless the yarn has been engineered around that trade-off.

Colour behaves counter-intuitively in solar shade fabric. A dark fabric absorbs light rather than scattering it, so it cuts glare and preserves a crisp view out. A light fabric reflects solar energy away from the glass, so it controls heat — but it also scatters light inside the weave, which is what makes a white shade look washed out and hazy in bright sun.

So the conventional choice is between a dark fabric with a good view and poor heat rejection, or a light fabric with the reverse. Dual-sided satin weaves address this by putting white on the street side and a darker colour on the room side.

KOOLBLACK® Technology addresses it in the yarn itself: it is engineered to keep the view-through of a dark fabric while rejecting substantially more heat than a dark fabric normally would. That is the reason to reach for a high performance fabric rather than a conventional one.

Reading a fabric spec sheet

Rs, As and Ts always add to 100%. Once that clicks, a mill spec sheet stops being a wall of abbreviations.

Every mill spec sheet reports the same core values. Solar energy hitting the fabric is either reflected (Rs), absorbed (As) or transmitted (Ts), and those three always total 100% — that is the RAT equation. Reflectance is the one doing the useful work: energy reflected back out never becomes heat in the room.

The same split is reported for visible light alone, as Rv and Tv, because what the eye does with the light and what the building does with the heat are different questions.

SHGC — solar heat gain coefficient — is the number that matters for the building: the proportion of solar energy that reaches the interior. It is a property of the glass and the shade together, not the fabric alone, so a fabric SHGC is only meaningful alongside the glazing it was measured against.

Full definitions for all seven values are on the fenestration reference.

Choosing by exposure

Which way the glass faces changes the answer more than the climate does.

Orientation determines the geometry of the problem. South-facing glass takes high-angle sun for most of the day, which a shade intercepts efficiently. West-facing glass takes low-angle sun straight down the sightline for the last hours of the working day — the hardest glare condition in a building, and the one that drives complaints.

East glass has the same low-angle problem in the morning, when fewer people are at their desks and it is more often tolerated. North glass in the northern hemisphere gets no direct sun at all; the requirement there is usually brightness and privacy, not solar control.

Climate modifies the answer rather than setting it. A cooling-dominated climate rewards reflectance; a heating-dominated one may want winter solar gain retained, which argues for a higher openness or an operable system that can be scheduled.