NOVELTY - The multilayer material comprises a layer (20) having a variable reflection, a variable crystallographic structure and a variable surface morphology, which varies reversibly as a function of a temperature, an infrared reflective layer such as a layer made of aluminum, copper or gold having a thickness of 10 nm, a diffusion barrier layer, a mechanically resistant material covered with a reflective layer, and an infrared reflector. A parameter of surface roughness is greater than a first roughness value (0.3-2 microns) when the temperature is lower than a threshold temperature.    USE - The multilayer material is useful for producing a solar panel including an absorbent member (claimed), where the panel is a thermal solar panel.    ADVANTAGE - The multilayer material is capable of efficiently and economically producing the thermal solar panel with high absorbency, low emissivity, improved performance and enhanced mechanical strength.    DETAILED DESCRIPTION - The multilayer material comprises a layer (20) having a variable reflection, a variable crystallographic structure and a variable surface morphology, which varies reversibly as a function of a temperature, an infrared reflective layer such as a layer made of aluminum, copper or gold having a thickness of 10 nm, a diffusion barrier layer, a mechanically resistant material covered with a reflective layer, and an infrared reflector. A parameter of surface roughness is: greater than a first roughness value (0.3-2 microns) when the temperature is lower than a threshold temperature; and less than a second roughness value ( less than or equal to 0.1 mm) when the temperature is greater than the threshold temperature, where the second value of roughness is less than the first value of roughness. The layer having the variable surface morphology is covered with an absorbent layer (30a) comprising a layer of absorbent material or a stack of absorbent material layers. The absorbent layer has an absorption coefficient of greater than 70% for wavelengths of 350-2000 nm, and a thickness of 10-500 nm. The reflection of incident radiation having a wavelength of 350-2000 nm: diffuses when the temperature is less than the threshold temperature; and is specular when the temperature is greater than the threshold temperature. The layer has: mother phase such as austenitic that is stable when the temperature is grater than the threshold temperature; and daughter phase such as martensitic obtained from a displacive transformation of the mother phase. A thickness of the layer having variable surface morphology is 500 nm to 400 mm. An emissivity of the multilayer material is less than 15% for wavelengths of 7-10 mm. The absorbent layer is made of a thermochromic material of which a transmittance in the infrared is: greater than a first transmission threshold (greater than 80%) when the temperature of the thermochromic material is less than a critical temperature; and less than a second transmission threshold (less than 15%) when the temperature of the thermochromic material is greater than the critical temperature, where the second transmission threshold is less than the first transmission threshold. A difference in absolute value between the second and first threshold is 25-80%. The diffusion barrier layer is made of an oxide material such as silicon or aluminum oxide, and has a thickness of 1-10 nm. The threshold temperature and/or critical temperature is 60-120 degrees C. The absorbent layer is covered with a layer of antireflection material having a thickness of 20-150 nm. The layer forms a variable mechanical support for other layers. An uncoated side of the support is directly contacted with a coolant fluid. The support is flat, tubular or curved support.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a multilayer material.    Aluminum support (10)    Layer having variable surface morphology (20)    Absorbent layer. (30a)