Why do extension cord insulation ratings matter, and what rating should I look for?

Ignoring insulation ratings can start a fire. The rating (60°C, 75°C, 90°C, or 105°C) is the max temperature the insulation can handle before failing. Cheap indoor cords are often 60°C, but ambient heat from sun or tools can exceed that. For any cord that might see heat—garage, workshop, outdoors—get one rated at least 90°C, like SJTW or SJTOW cords.