NOVELTY - The paraboloid and planar mirror comprises a laminate of a transparent front cover (a), sunlight-reflecting layers (b), 20-30 wt.% of plasticizer-containing polyvinyl acetal film (c) and a back cover. The plasticizer-containing polyvinyl acetal film contains polyvinyl acetal with a polyvinyl alcohol content of less than 20 wt.%. The plasticizer-containing polyvinyl acetal film has: a creep tendency determined on a laminate with a structure comprising 3 mm float glass, 0.76 mm film or 3 mm float glass at a temperature of 100 degrees C after 7 days; and a moisture content of less than or equal to 1.5 wt.%.    USE - The paraboloid and planar mirror is useful for solar thermal power plants or Fresnel collector system, and as linear concentrator.    ADVANTAGE - The paraboloid and planar mirror exhibits low creep of the adhesive layer and low corrosion of the specular surface.    DETAILED DESCRIPTION - The paraboloid and planar mirror comprises a laminate of a transparent front cover (a), sunlight-reflecting layers (b), 20-30 wt.% of plasticizer-containing polyvinyl acetal film (c) and a back cover. The plasticizer-containing polyvinyl acetal film contains polyvinyl acetal with a polyvinyl alcohol content of less than 20 wt.%. The plasticizer-containing polyvinyl acetal film has: a creep tendency determined on a laminate with a structure comprising 3 mm float glass, 0.76 mm film or 3 mm float glass at a temperature of 100 degrees C after 7 days; and a moisture content of less than or equal to 1.5 wt.% after storage at 23 degrees C. A relative humidity (85%) for 24 hours is less than or equal to 1.8 wt.%. The polyvinyl acetal has a molecular weight of more than 110,000 g/mol. The hydroxyl groups (0.001-1%) present in the polyvinyl acetal react due to the crosslinking. The plasticizer has a polarity of less than or equal to 9.4. The plasticizer-containing films based on polyvinyl acetal have a plasticizer content of 18-32 wt.%. An INDEPENDENT CLAIM is included for a process for the manufacture of a mirror for solar thermal power production.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a paraboloid mirror.    Transparent front cover (a)    Reflective layer (b)    Film (c)    Rear cover (d)    Point. (e)