The white sands of Cancun are composed of fragments of shell and coral and are always cool to the touch. So if you walk barefoot in the midday sun no matter how hot the sand is always cool for your feet. Scientists are still perplexed by the mystery of Cancun sand.

Have you ever tried to walk on the sand of beaches in other parts of the world barefoot? Ouch! Not here! Walk for miles and miles.

Those beaches from the town to Punta Cancun (the center of the hotel zone) face Isla Mujeres so waters tend to be calm and child-safe as the waters are sheltered. The ocean here is shallow and calm.

However the water on the open-side of the hotel zone of Cancun from Punta Cancun to Punta Nizuc which is just the opposite. Characterized by pounding surf and strong currents, care should be taken. Mind you the views are awesome. The undertow on these beaches may be quite strong.
Always check the warning flags posted on the beach in front of the hotels. Red or black means dangerous conditions. You ask why two different colors to signify the same thing?  Good question. Sometimes one color gets lost. Yellow indicates precaution and not may be some warm spots. Green or blue indicate ideal swimming conditions.

Some public access beaches in the northern part of the hotel zone where waters are calm are Playa Las Perlas next to Hotel Imperial Las Perlas. Playa Tortugas. Playa Caracol, Playa Juventud, and Playa Linda. 

Beaches on the open ocean in the southern part of the hotel zone are Chac Mool, Playa Marlin, Ballenas, and Playa del Rey (Delfines or Mirador).

The beaches become quite crowded on Sundays and holidays.

Strong winds blowing in from the Caribbean can change the coastline. Waves breaking on a beach at a certain angle can erode the sand and deposit it further north or south hence some beaches may become narrower and others wider.