This study analyzes the depth of self-disclosure in the interpersonal communication of 11-3 grade Visual Communication Design (DKV) students at SMKN 9 Medan using Irwin Altman and Taylor's Social Penetration Theory. Through a descriptive qualitative approach, data were collected from 10 informants divided into five friendship dyads using in-depth interviews, observation, and document studies. The results showed that students' interpersonal communication processes gradually developed, penetrating the six layers of Social Penetration Theory, from the biographical layer, preferences, aspirations, values and beliefs, private issues, to the core self-concept. The achievement of this penetration depth was divided into two categories, groups that managed to fully penetrate all layers thanks to long lasting friendships, high reciprocity, and psychological safety, and groups that experienced partial penetration due to the application of privacy boundary management and past friendship trauma. This dynamic shapes a circular communication pattern driven by risk perception, relational roles, cultural values, and emotions. The study concludes that full penetration contributes to the development of absolute trust and nonverbal sensitivity, while partial penetration serves as a self-protection mechanism to maintain harmony in social interactions at school