Hail damage is a common problem. Common examples include broken glass in greenhouses and dents on cars. The TNO hail simulator can be used by suppliers of plastics, glass and metal roofing materials to assess the risk of hail damage. TNO has over 30 years' experience in the field of hail damage research for horticultural greenhouses.

Research with the hail simulator at TNO is carried out with nylon 'hail,' mostly with a diameter of 20 mm or 30 mm. In the standard configuration, the simulator can test materials with a width of 1.5 m and a height up to 20 cm. For larger pieces, the test apparatus is extended with a projecting arm. The simulator can move along both the X and Y-axes, which means that the material being tested can remain stationary.

Test procedure

During the test, the 'impact' damage is monitored closely. The results can be compared with those of previous tests on a number of reference materials.

During a hail shower there may be differences in the velocity at which a hailstone of a certain dimension falls. In the interest of safety, the hailstone resistance testing can be based on the highest velocity at which a spherical hailstone can fall. As the kinetic energy at the final velocity is known, it is then possible to estimate the maximum hailstone diameter to which the test material is resistant. If requirements for hailstone resistance are not laid down in standards, TNO can advise you in preparing a test and evaluation protocol for the product in question.


The Hail Simulator is suitable for testing products such as:

  • Siding
  • Roofing materials
  • Caravans
  • Plastic gutters

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