Jacket and trousers are preferred in different thicknesses.
Generally, especially when we approach spearfishing for the first time, we tend to choose wetsuits with a specific thickness, 3.5, 5, 7 and 9 mm, or in between such measures, with the same values for jacket and trousers. With tim and experience we find out, though, that often it is better to wear a thicker jacket, as this protects the central part of the body and its vital organs, while trousers can be thinner, to be able to move more freely and use less weight.
Many companies, for such reason, offer the possibility to buy separately jacket and trousers, to give the customer the freedom to choose different sizes and thicknesses.