Neither flat nor round extension cords belong under a rug.

Neither. Flat cords are less of a tripping hazard, but the real danger isn’t the shape — it’s the rug. Cords under rugs trap heat, get walked on, and get damaged without you noticing. Damaged cords cause fires.

Flat cords are slightly better at distributing pressure, but they still overheat under a rug. A rug is an insulator. That heat has nowhere to go. The cord heats up, the insulation weakens, and now you have a fire risk you can’t see.

If you absolutely must run a cord across a floor, get a proper floor cord cover — the rubber speed-bump kind. Otherwise, rearrange the room or use a shorter cord. This is not where you save six bucks.