Each door is custom-made to your size and requirements. Thermally broken on the whole system, including the threshold. The class-leading U-values are provided on the whole unit, not just the door panels, so that you know exactly what you are getting. U-values range from 1.4 with double glazing down to 0.79 with triple glazing and the best specification. You expect your bifold doors to slide effortlessly from the day one. But you also want them to be equally effortless 10 years later. The stresses on a bifold door are considerable — and only doors engineered to such a high standard will last the distance. Topbright doors are tested to 20,000 cycles — the equivalent to opening twice a day, every day for 27 years!