It was claimed that the natural color of the enamel would be assumed in from a few days to a week or more, the natural color of the tooth would be restored, and that considerable strength was obtained, owing to the nonfriability of the enamel.
Source: wiktionary
This gives whiskers a degree of toughness and nonfriability not found in any other reinforcements.
Source: wiktionary
of about 3 percent, and an exceptionally high degree of toughness and nonfriability -- along with greater abrasion resistance than any other fiber on the market today.
Source: wiktionary