Greece has the same water conditions as here (Sardinia). I dive with a 3mm superstretch lining. This is warm enough. An open cell suit will be warmer still than this.
For freediving in a pool 3mm will be too much (just wear half the suit). For freediving in Sweden, lake or sea, 3mm will not be enough, except in the summer.
For freediving in a pool 3mm will be too much (just wear half the suit). For freediving in Sweden, lake or sea, 3mm will not be enough, except in the summer.