Non-invasive brain stimulation (NIBS) techniques, such as transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES), hold promise for treating various neurological disorders. However, the efficacy of these techniques depends significantly on understanding the transfer function of the skull and other intervening layers for current density. This study provides a comprehensive review of the histological and electrical properties of the skin, fat, skull bone, dura mater, arachnoid layer, cerebrospinal fluid (CSF), and pia mater, which form the pathway for electrical currents in NIBS. By examining the equivalent circuit models of each layer, we highlight the resistance, capacitance, and impedance characteristics that influence current propagation. Key findings include the high impedance of the stratum corneum in the epidermis, the significant capacitance of the skull bone, and the variable conductivity of CSF. Computational models reveal that these layers collectively affect the distribution and intensity of electrical currents reaching the brain. Understanding these properties allows for optimizing NIBS parameters, potentially enhancing therapeutic outcomes, and minimizing side effects. This study underscores the importance of detailed anatomical and electrical modeling in the advancement of effective NIBS therapies.