SJOOW is the best jacket for extension cords.

Yes, it matters — but only if you’re using the cord outdoors, in a shop, or anywhere it’ll see abuse. For light indoor use, you probably don’t need to care.

The letters tell you everything. S = Service grade. J = Junior (lighter duty than SO, fine for most household use). Second part is the jacket material: O = oil-resistant, W = weather-resistant. So SJOOW is oil-resistant and weather-resistant. SJTW is thermoplastic (PVC) and weather-resistant — no oil resistance.

SJOOW stays flexible in the cold, shrugs off oil and gas, and doesn’t crack after a few seasons in the sun. SJTW gets stiff, cracks faster, and if you drag it through a puddle of motor oil, the jacket will degrade. For contractor jobs, garages, or anywhere you’ll drag it over concrete and sharp edges, SJOOW is worth the extra money.

For a string of Christmas lights or a lamp in the living room? SJTW