There is one question that comes up in almost every curtain fabric procurement conversation for hospitality: should this space have blackout or dimout? For guest rooms the answer is almost always blackout. For everything else (lobbies, corridors, meeting rooms, F&B spaces), dimout or light-filtering is the specification. But the technical difference between the two is wider than most buyers realise, and specifying the wrong one creates problems that do not become visible until the curtains are installed.
What "blackout" means technically
A blackout curtain fabric achieves 0% light transmission. This is a measured physical property, tested to EN 14272 or ASTM D1003, not a marketing claim. The construction that achieves 0% transmission is typically a woven polyester face fabric bonded to a white flocked acrylic backing; the backing blocks all light transmission while the white surface reflects solar radiation back through the glass. Most commercial blackout fabrics in the 280–310 GSM range use this construction.
The 0% figure is binary: either a fabric achieves it or it does not. Fabrics described as "99% blackout" or "near-blackout" do not achieve 0% transmission. In a hotel guest room, 1% residual transmission creates a visible glow at the track gap and along the header at dawn, and guests notice it before they notice anything else in the room. Specify 0% or specify it correctly as dimout.
The white acrylic backing serves a second purpose in GCC climates: it reflects incoming solar radiation back through the glass, reducing the thermal load on the room and lowering cooling costs. This is why white-backed blackout is the standard construction for UAE, Saudi Arabia, and Qatar hotel projects, not an arbitrary preference.
What dimout means
Dimout fabric achieves 3–8% light transmission, sufficient to significantly reduce incoming daylight while retaining a soft luminosity in the space. Dimout fabrics use a lighter backing construction (typically a thin foam layer or partial acrylic coating) rather than the full flocked backing of blackout. Weight is correspondingly lower: dimout fabrics typically run 200–240 GSM against blackout's 280–310 GSM.
The practical effect is that a dimout space in daylight reads as diffuse, even light, with no visible sky through the fabric, but no darkness either. This is the correct specification for lobbies, corridors, meeting rooms, and F&B spaces where total darkness would be architecturally wrong but uncontrolled glare would be uncomfortable. Dimout also allows for a greater range of face fabric textures and appearances, which is why linen-look and textured constructions are predominantly dimout or light-filtering rather than blackout.
Where each belongs in a hotel
| Space | Specification | Reason |
|---|---|---|
| Guest rooms and suites | Blackout (0% transmission) | Sleep quality; shift workers; time zone adjustment |
| Serviced apartment bedrooms | Blackout | Same as guest rooms |
| Hospital patient rooms | Blackout | Clinical requirement; recovery sleep |
| Cinemas, screening rooms | Blackout | Technical requirement |
| Hotel lobbies | Dimout or light-filtering | Visual openness; brand atmosphere |
| Corridors and public areas | Dimout | Safety: exits must remain visible |
| Meeting and conference rooms | Dimout (+ motorised for AV) | Daylight control without full blackout |
| F&B and restaurant spaces | Light-filtering | Atmosphere; solar control |
| Spa and wellness areas | Dimout or blackout depending on treatment type | Treatment-room blackout; relaxation areas dimout |
FR certification: how it applies to each construction
Both blackout and dimout fabrics can be produced to FR certification. The M1, BS 5867, and EN 13773 standards apply to both construction types. What changes is the backing, and this matters for certification scope.
Blackout fabrics have a heavier white acrylic backing. This backing must be included in the FR certification: the test must cover the complete assembled construction (face fabric plus backing), not the face fabric alone. A certificate that covers only the face fabric of a blackout construction is not a valid FR certificate for the blackout product.
Dimout fabrics with lighter backing require the same scrutiny: the FR test must cover the complete construction. The thinner backing on dimout fabrics means FR performance can vary more between constructions; always request the test report for the specific product, not a generic range certificate.
For hotel curtains cleaned regularly by housekeeping, inherently FR fabric is the only correct specification for both blackout and dimout. Topically treated FR loses its fire-retardant property after 20–50 wash cycles. The FR performance of inherently FR fabric is permanent for the life of the fabric: it cannot wash out because it is built into the fiber chemistry, not applied to the surface.
Weight, construction, and cost
Blackout typically runs 280–310 GSM. The additional weight comes from the full acrylic backing; the face fabric weight is similar between blackout and dimout. Dimout typically runs 200–240 GSM. The weight difference has practical implications: blackout requires heavier track systems and stronger header construction, particularly for wide-width panels (280–300 cm).
On a per-meter basis, dimout is typically 15–20% less expensive than blackout due to the lighter backing construction. For large projects where some spaces can be correctly specified as dimout rather than blackout, this is a meaningful budget difference at scale.
The short specification guide
Specify blackout fabric (0% transmission, 280–310 GSM, white acrylic backing, M1 or BS 5867 certified) for: any room where guests sleep, any space requiring complete darkness as a functional requirement.
Specify dimout (3–8% transmission, 200–240 GSM, partial backing, BS 5867 or EN 13773 certified) for: all other hospitality spaces requiring daylight control, any space where a sense of natural light is desirable, all corridors and public circulation areas.
If in doubt about a specific space (particularly mixed-use areas or branded hotel suites with integrated living rooms), default to blackout for the sleeping zone and dimout for adjacent living areas with separate track systems.