Flat extension cords vs round extension cords: Flat wins under rugs, but only if rated for it

Flat cords are thinner and dissipate heat better, making them safe under carpets if specifically listed for it — round cords trap heat and are a fire hazard when covered. But flat cords typically carry less current (13 amps vs 15 amps), so don’t run high-draw devices like space heaters through them. For baseboard runs, either works, but round is more durable for visible, long-term use.