The shell of the helmet shall be made of materials that are hard and durable. Many materials are in existent for suitable, but we were already recognized that thermoplastic resin is spoilt by ultraviolet rays in sunshine.

Our outdoor weathering was given period of time, which are O, 3, 4.5, 6, 7.5, 9, 10.5, 12 months.

Materials made an experiment on falling weight test, compression test, hardness test. Falling weight test as follows:—

The shell mounted on the fixed steel plate, the 3.6 or 2.7 kg steel ball shall be dropped vertically on the center of the shell from a height of 1.3m measured from the bottom of the shell.

On falling weight test, 7.5 month's exposed PE and ABS, 12 month's PC was broken down,another test showed weakened conditions.