Due to the global spread of infectious diseases, telework has become increasingly prevalent. However, the reported results have been mixed regarding the effectiveness of telework. This study examined whether the relationship between telework and work-family conflict would be changed by the permeability and flexibility of the border around work. Study 1 validated Clark’s (2002) scales of permeability and flexibility characteristics of each work-family border. The scales were first translated into Korean, then back-translated into English to examine item-consistency of the scales. The results of exploratory factor analyses based on 219 Korean working adults showed that the border around work and the border around family each consisted of two factors: permeability and flexibility. Additionally, correlation and regression analyses were conducted to examine the nomological network of the scales using the theoretically relevant predictors and criteria. Study 2 examined border characteristics around work to investigate whether permeability and flexibility moderates the relationship between telework and work-family conflict. A survey was conducted on 250 teleworking Korean adults which showed that flexibility did not moderate the relationship between telework and work-interfering-family. However, the positive relationship between telework and family-interfering-work increased when flexibility was low. This study suggests that organizations should provide flexibility in the border around work, to alleviate the negative impact of work-family conflict on teleworkers during the post COVID-19 period.