The U. S. penny is made primarily of zinc. There have been several times in recent years when zinc prices have been high and it has cost the U. S. Treasury more than one cent to manufacture a penny. There are currently about 1.4 billion pennies in circulation. Economist François Velde of the Federal Reserve Bank of Chicago has proposed making the current penny worth 5 cents.
Source: Austan Goolsbee, "Now That a Penny Isn't Worth Much, It's Time to Make It Worth 5 Cents," New York Times, February 1, 2007. The effect of this proposal would cause the value of M1.