We started with the gap, not the fabric.
Most blackout blinds are sold on the material. Hold it up, no light passes through, job done. Then you fit one, close it on a bright morning, and there it is — a bright line at the top, a glow down each side, daylight under the bottom bar. The fabric was never the problem.
BLOCKER exists because that gap is the interesting part of the problem, and because solving it properly means treating the window as a whole opening rather than a rectangle of cloth.
What that means in practice
Every BLOCKER is made from the measurements of one specific window. Not the nearest standard size, not a width rounded to the closest 50mm — the recess you actually measured, in six places, because recesses are rarely square.
The perimeter is treated as functional, not decorative. The frame and edge channels are there to control the space around the blind, which is where light usually gets past a conventional roller.
How we talk about the product
We would rather explain what BLOCKER is designed to do than promise an absolute. You will not find a percentage on this site that we cannot stand behind, or a claim about your sleep that belongs to a doctor rather than a blind maker.
Where something depends on your particular window, we say so and ask you to check. Where we have not confirmed a specification yet, we leave it out rather than guessing. That is a slower way to sell a blind. It is a better way to end up with one that fits.
Before you order
The single most useful thing you can do is check the window before you buy. Read the measuring guide, look at the window types page, and if anything about your recess looks awkward, send us photographs before we make anything.