Is the adidas SW 5540 waterproof?

No. It has a leather upper and textile lining but no Gore-Tex or waterproof membrane, so it handles dew and light damp but not steady rain.

How does Boost compare with other golf shoe midsoles?

Boost is softer and springier than the firm EVA used in most spikeless shoes. That helps comfort when walking but gives a little less stability on aggressive swings.

Are spikeless shoes like this good for walking 18 holes?

Yes. The Boost cushioning and leather upper are built for comfort, and the rubber outsole flexes with the foot. Traction is the trade-off on wet or steep lies.

What sizes and width does it come in?

It comes in US men's sizes from 8 to 13 in half sizes, in a normal width. The laced closure lets you adjust the fit.

Can I wear these off the course?

Yes. The spikeless rubber outsole is fine on paths, in the clubhouse and driving, which is the main reason golfers pick spikeless over spiked shoes.

How should I clean the white leather upper?

Wipe it with a damp cloth after each round and use a leather cleaner for scuffs. Avoid machine washing, which can damage the leather and Boost midsole.