Choosing between 3W/m·K and 5W/m·K IMS PCB material depends on more than thermal conductivity. Engineers should consider heat density, thermal margin, dielectric thickness, copper spreading, metal-base construction and the complete thermal path. This guide explains when 3W/m·K is sufficient, when 5W/m·K provides meaningful thermal benefits, and how to make a more efficient IMS material selection for real-world PCB designs.