imperviumn.

1932 P. Nowlan Buck Rogers in Oakland (Calif.) Tribune Comics 18 Dec. 1/3 I hardly thought the telescope would penetrate the impervium walls of the tower.

1933 P. Nowlan Buck Rogers in Syracuse (N.Y.) Herald 27 Mar. 14/2 The hull is made of impervium—thousands of times harder than any other substance.

1943 Astounding Sci.-Fiction Mar. 9/1 A half mile beneath the shallow Venusian sea the black impervium dome that protects Montana Keep rests frowningly on the bottom.

1957 Poetry Sept. 374 Come, marry the bottom of our minds. Grant us the strength of your impervium.

1989 Jrnl. Nucl. Materials 167 4/1 The CeS crucibles that we had developed were found to be so highly resistant to attack..that we thought the ‘Impervium’ crucibles could contain any molten metals.

1991 D. Drake Jungle x. 96 Light flickered from the zenith of the impervium dome and reflected even here.

2005 W. McCarthy To crush Moon iv. 61 Our armor was struck by multiple projectiles—five-gram impervium wirebombs.