length of the inflator 126 until contacting the bumper guard 136 the sliding cylinder 134 and attached tensioning tether element 137 are thereby moved from the position illustrated in fig2 a to the orientation illustrated in fig2 b simultaneous with the downward movement of the inflatable curtain 110 and the accompanying vertical force component applied to the tensioning tether element 137 the inflatable curtain 110 also undergoes a degree of shortening as inflation takes place this shortening gives rise to the application of a substantially horizontal force component to the tensioning tether element 137 it is believed that the ability of the tensioning tether element 137 to move downwardly in conjunction with the inflatable curtain 110 as both vertical and horizontal tensioning forces are applied permits the tensioning tether element 137 to be maintained in a state of tensioned dynamic equilibrium during the inflation event while nonetheless using a tether which is of substantially fixed length in fig3 a and 3b there is illustrated a variant to the assembly illustrated and described in relation to fig2 a and 2b in fig3 a and 3b elements corresponding to those previously illustrated and described are designated by like reference numerals increased by 200 as best seen by simultaneous reference to fig3 a and 3b in this embodiment the tether tensioning device 225 is arranged such that the inflator.