The availability of and preference for eco-friendly products have increased; however, understanding of sustainable products is still insufficient because most studies have been focused only on organic products. The availability and understanding of organic products are high, but not complete. With regards to environmental protection, it is important to focus not only on the eco-friendly ingredients but also on the eco-friendly packaging because packaging has recently been found to be a primary cause of pollution. Through three studies, this article investigated the interaction between the effect of consumers’ willingness to buy (WTB), the price premium for eco-friendliness (internal: eco-friendly ingredients vs. external: eco-friendly packaging), and the product’s attributes. Three experimental studies were conducted to determine whether the consumers’ WTB and the price premium for sustainable products differ according to the eco-friendliness of the product and the product’s attributes. In Study 1 and Study 3, analysis of variance (ANOVA) was conducted; and, in Study 2, analysis of covariance (ANCOVA) was conducted. The results of Study 1 and Study 2 suggested that the consumers’ WTB for sustainable products can differ according to the product’s attribute. Moreover, results of Study 3 revealed that consumers’ WTB and satisfaction for sustainable products can differ according to level of packaging.