Is the Nike Air Force 1 Low SP UC actually waterproof?

Yes. It uses a Gore-Tex membrane under a leather upper, so it keeps water out in rain and slush. It is watertight, not a rubber boot, so deep puddles can still come over the top.

How does it compare with a regular Air Force 1 Low?

Same silhouette and Air-Sole cushioning, but the SP UC adds a Gore-Tex lining and a heavier, stiffer build. You give up breathability for weather protection.

Does it fit true to size?

The Gore-Tex lining makes it feel snugger than a standard leather AF1. If you are between sizes or have wide feet, going up half a size is the safer call.

Is it good for summer?

Not really. The waterproof membrane traps heat, so it is better suited to fall, winter and rainy spring days than hot weather.

How should I clean the white upper?

Wipe with a damp cloth and mild soap, and brush off salt stains before they set. Avoid soaking the shoe, since the membrane does the waterproofing work.