Why it is so important Widely respected for its expertise in high-end aluminium glazing products, Fenster was approached by programme-makers and asked to supply a premium-quality sliding door. Founded in 2006, Fenster is one of the West Country’s leading aluminium suppliers. In addition to offering the full range of products from Smarts, the company also manufactures Üni_Slide, an ultra-slim aluminium sliding door, equally suited to commercial and residential applications.