BlocOut blinds as the name suggests offers a 99.9% darkness to a window. Here a little of what the manufacturer (Bloc) has to say about them.
Bloc Domestic Cassetted Black-Out System Highly innovative roller blind system. It combines an aluminium cassette and precision engineered side rails to create a blind that can block out light and draughts. All fabrics are 99.9% Black-Out (not just dim-out)
This in turn provides significant savings on home heating costs and when combined with the right fabrics, can bring a space complete and total darkness. These possibilities bring this range of blinds an added functionality that is just not possible to achieve with any other blind currently on the market.
The first blind to have been independently thermally tested by the BBA and has been proven to save at least 25% on average heating costs. This product is the only 'domestic' cassetted FULLY BLACK-OUT system on the UK market today.