Impenetrable, as in impervious to rain; incapable of being injured or impaired, as in impervious to wear and tear; incapable of being persuaded, influenced, or affected, as in impervious to another person’s suffering.
Over the past several years, car buyers have been spoiled by the generous cash-back and low-interest offers that dealers were slapping on pretty much any car in the lot.
"People became addicted, but also impervious to those incentives," says Robert Gentile, director of car information products at Consumer Reports. As incentives became a less-effective marketing tool to drive buyers to the dealerships, the manufacturers naturally tried to trim wide-scale promotions. This was yet another reason for the sales slump this summer.
—Aleksandra Todorova “Timing a Car Purchase” Wall Street Journal, August 26, 2007