A penetration into the fabric is a typical defect which appears when plastic is injected over textile and it is able to pass through the fabric to reach the aesthetic side of the part. Once that penetration takes place, the faulty piece is rejected and a possible solution to eliminate the defect is the trial and error process, changing successively the injection parameters, and therefore increasing the production costs. For that reason, it is very important to characterize these penetrations in order to anticipate the injection conditions that cause the defect and consequently, to optimize the overmolded injection process, reducing to the maximum the number of rejected pieces. In this article, the work consists of designing a methodology to combine injection parameters and fabric tension that causes the penetration that appears to characterize them. The combination of minimum tension, minimum injection temperature, and minimum injection pressure in the exact point in which defect appears will characterize the penetration. POLYM. ENG. SCI., 51:1848-1857, 2011. (C) 2011 Society of Plastics Engineers