Extension cord insulation ratings are not marketing fluff.

Yes, they matter a lot, and ignoring them can start a fire.

Every extension cord has a temperature rating printed on the jacket — typically 60°C, 75°C, 90°C, or 105°C. That number is not a suggestion. It’s the maximum temperature the insulation can handle before it starts to soften, crack, or melt. When you run a cord in a hot environment — like near a furnace, under direct summer sun on a black driveway, or in an attic — the ambient heat adds to the heat generated by the electricity flowing through the wire. If the combined temperature exceeds the rating, the insulation fails.

Cheap indoor extension cords are often rated 60°C. That’s fine for a lamp in your living room. But set one on a sun-baked concrete patio in July, and the surface temperature can easily hit 60°C before you even plug anything in. Then add the heat from a running circular saw or a space heater, and you’re cooking that cord from both sides. I’ve seen cords go soft and sticky, which is a few steps short of a short circuit and a fire.

For any cord that might see heat — garage, workshop, outdoors in summer — get one rated at least 90°C. SJTW or SJTOW cords usually meet that. The extra