The stress areas such as the toe or panty portion have been strengthened with yarns of heavier denier.

given added strength or support; "reinforced concrete contains steel bars or metal netting"

concrete Steel rods are inserted in concrete beams to help them withstand longitudinal stress without collapsing. This development has allowed the construction of very large structures using concrete beams.

(used of soaps or cleaning agents) having a substance (an abrasive or filler) added to increase effectiveness; "the built liquid detergents"

It indicates that the tyre has been reinforced. Tyres with this indication are usually used for equipping transport vehicles derived from motor cars.

A weakened stamp which has been given protective support.