As long as you don't go into the water before, wearing a long-sleeved swimsuit is definitely warmer than a short-sleeved swimsuit, because the long-sleeved swimsuit can cover more meat, but once you go into the water, the actual effect is the same and it will be colder.

When swimming, long-sleeved swimsuits will be more laborious because of their large contact area with water, mainly depending on their own needs.

But it does not keep warm after entering the water.

Generally speaking, wearing a swimsuit before entering the water can help people keep warm, but once in the water, because the body is wet, once in the water, wearing a swimsuit can't keep warm, but it will absorb the heat of the whole body, causing the human body to get colder and colder, just like sweating and changing clothes for minutes to catch a cold, so wearing a swimsuit once in the water will not keep warm.