By Dominic Laurie
Europe business reporter, BBC News, Brussels
The EU has fined five companies almost 250m euros ($366m; £180m) for fixing the price of the rubber used to make everything from shoe soles to condoms.
Chloroprene rubber is used to make products such as condoms
A sixth firm was let off because it had blown the whistle on the cartel to European Union investigators.
Chloroprene rubber goes into all sorts of everyday household products. It stretches under stress, but returns to its original shape afterwards.
Regulators estimate consumers have been overcharged by between 10% and 30%.
The cartel operated between 1993 and 2002, during which time the firms colluded to set each others' market shares and prices, the European Commission concluded.
According to regulators, the companies held "regular meetings to discuss prices (and) exchange sensitive commercial information".
The six firms named by the Commission make 100% of the product sold in the EU.
The Italian firm Eni received the largest fine - more than 130m euros.
The penalty was increased by 60% from the original amount levied because it was the third time Eni had been caught by EU regulators.
Germany's Bayer had its 200m euro fine scrapped because it was the first of the six to own up to any wrongdoing.
US firms DuPont and Dow Chemical were fined 59.3m and 48.7m euros respectively, enjoying a 25% reduction in their fine because they cooperated with investigators.
Japan's Denka was fined 47m euros while Tosoh, also from Japan, saw its fine halved to 4.8m euros because it too helped the authorities.
Under EU law, the Commission can fine companies found guilty of price-fixing up to 10% of their worldwide annual turnover.
The Commission said this was the third time that the rubber industry had been caught engaging in price-fixing.
Competition Commissioner Neelie Kroes said it was "particularly disappointing (that the industry) has still not learned its lessons about avoiding cartels".