addition the plates are preferably about 1 mm to about 5 mm thick the plates are also preferably made of a plastic material with relatively high heat distortion temperature and low flammability padding 9 on the interior surfaces of the inner set of plates is shown to be substantially thicker than that of the rigid members themselves it is contemplated herein that in one embodiment padding 9 is not present the padding is however present in a preferred embodiment padding 9 may also be on the interior surface of all the inner set of plates if desired the padding is preferably flame retardant resistant to the penetration or absorption of liquids and is about u00bc inch thick plates 8 are shown in an overlapping configuration so that the gaps in one layer or set are covered by the plates in the other layer this may be referred to as an u201c armadillo effect u201d because as the invention expands or contracts there is always at least one plate layer over the entire surface so that no gap is exposed referring now to fig3 a perspective view of a flattened envelope is shown wherein hook and loop fastener strips 10 are used as the means to attach the device to an existing helmet these strips can be sewn or otherwise attached to the envelope itself referring now to fig4 a front view of the preferred shape of a plate 11 is.