When sourcing ESD (Electrostatic Discharge) casters, the most vital specification is surface resistivity, which typically must fall between 10^3 to 10^9 ohms to ensure proper grounding. You should prioritize conductive materials like conductive rubber, polyurethane (PU), or nylon. Additionally, verify the load capacity per wheel (ensuring a 25% safety margin) and the bearing type, such as precision ball bearings, to ensure low rolling resistance in sensitive cleanroom or electronic assembly environments.