The benefits
Full darkness for better sleep at any time of day, which is why blockout is the go-to for bedrooms, nurseries and the homes of shift workers. Complete privacy, day and night, because nothing shows through the fabric. And a cooler room, since a backed blockout reflects heat rather than letting it build up through the glass.
A blockout fabric blocks light through the fabric, but a small amount always slips around the edges, because every roller blind is made slightly narrower than the window opening so it can roll freely. This is true of any roller, not just ours. How much edge light you get comes down to the fit: a face fit, on the wall outside the opening, reduces those side gaps far more than a reveal fit inside the recess, which always leaves gaps.
A reverse roll sits the fabric closer to the glass for less bleed again. If total blackout matters, in a nursery or media room, that fitting choice matters as much as the fabric, and it's exactly what an in-home measure sorts out.
