The paper details the development of a Korean style loungewear based on traditional Korean hanbok clothing. For this, we surveyed and collected data from 3,500 adults over 20 years of age. The questions were on their preferences of hanbok for both traditional and contemporary styles as well as loungewear. The survey showed that preferences for hanbok were high for both traditional and contemporary styles. The survey also suggests how a successful mass-produced Korean style loungewear should be designed to increase its popularity. It should feature comfortably simplified silhouettes, a selection of contemporary colors from Korean symbolic colors, modernized Korean textile surface designs, and easy-to-maintain healthy fabric. Based on these results, the development direction of Korean style loungewear was set and various loungewear samples were produced. Another group of survey participants were asked to try on samples and their preferences were surveyed. At the conclusion, a version that was most preferred among the participants was obtained. We suggest one-piece style and two-piece style designs with silhouettes based on the characteristics of traditional Korean costumes. The preferred fabric for loungewear was natural and soft cotton. We suggest the necessity and effectiveness of loungewear made with environment-friendly hanji-fabric. The main colors for loungewear were selected based on survey: blue, red, white, and saekdong (color stripes). We made color combinations with the main colors then applied the textile surface designs. The traditional Korean patterns of Hangeul (Korean letters), taegeuk (yin-yang), geometric figures, and samjogo (three-legged crow) were also chosen, and then loungewear using the textile designs was developed. The results have been shown on the "Han Style Fashion Show" by Jeonju City and exhibited in the "Seoul Living Design Fair" and the "International Art & Craft Trend Fair" in COEX, Seoul.