This study underscores the importance of considering a medium's broader effects. Research demonstrates that a medium's perceived eco-harmful impact affects communication effectiveness because a medium itself can act as a constituent of the message. The current study, conducted in Sweden, explores managers' estimates of consumer eco-harmful perceptions of 10 paper- and electronic-based media. Managers tend to mis-estimate consumers' eco-harmful media perceptions; these estimates are driven by managers' eco-conscious attitudes. Further, advertising on more eco-harmful media is associated with irritating characteristics, while advertising on less eco-harmful media is associated with good and trustworthy characteristics. Managerial implications are given for communication effectiveness in contexts where environmental concerns are particularly relevant.