Comparative advertising is used in many product categories (Beard, 2016; Kalro, Sivakumaran, & Marathe, 2010) and, as such, many different arguments are used to highlight the competitive advantage of products. For example, McDonald’s advertises store hours that exceed Burger King’s store hours [1], BMW claims to provide better overall quality than Audi [2], and Verizon Wireless suggests it provides better network coverage than AT&T [3]. These examples show that comparisons used in marketing vary considerably in terms of the attribute used for comparison as well as in verifiability (i.e., whether consumers can or cannot verify the comparison prior to purchase) and concreteness (i.e., comparisons can be rather broad and vague or quite concrete). Research has only marginally examined the effectiveness of using such different product characteristics for comparative advertising. However, many studies have examined the effectiveness of comparative advertising as compared to non-comparative advertising (e.g., Donthu, 1998; Dröge, 1989; Jeon & Beatty, 2002; Jewell & Saenger, 2014; Pechmann & Stewart, 1990; Zhang, Moore, & Moore, 2011). Such studies reveal positive and negative cognitive and behavioral effects (e.g., Chang, 2007; Grewal, Kavanoor, Fern, Costeley, & Barnes, 1997). Positive effects occur because comparative advertising provides consumers with valuable information, thus leading to increased attention (Muehling, Stoltman, & Grossbart, 1990), which, in other contexts, has been shown to trigger activation (Kroeber-Riel, 1979). Negative effects are a result of consumers thinking that marketers are using comparative advertising to mislead them (Chang, 2007; Swinyard, 1981). In such cases, consumers might show reactance (a motivational reaction to offers, persons, rules, or regulations that threaten or eliminate specific behavioral freedoms) to regain their threatened freedom (Brehm & Brehm, 1981) of free product choice and opinion formation (Clee & Wicklund, 1980). Reactance can be situation-specific, but individuals also differ in their predisposition to show reactance (PSR; Brehm & Brehm, 1981). The type of product-related information that should be provided in a comparison has received little attention. In a basic study, Jain, Buchanan, and Maheswaran (2000) examine the effects of the verifiability of product characteristics. However, this categorization only roughly covers what is common in advertising practice because comparisons based on product attributes not easily verifiable prior to purchase can still be more or less concrete, and consequently vary in their effectiveness. Thus, the objective of this research is to examine the effects of concrete versus less concrete comparisons in advertising. We examine the positive effects of such comparisons through activation and the negative effects through reactance, and the possible moderating effect of consumers’ PSR. We also examine the effect of claim substantiation in terms of factual information that supports and legitimizes the comparative claim (McDougall, 1978).