The majority of divers wear wetsuits for thermal insulation, although in colder conditions a dry suit can be worn instead.
Wetsuits insulate the diver by providing a tight fitting layer of closed cell neoprene around the diver; all this means is that the wetsuit isn’t porous so you don’t get wet because of water flowing through the material of the wetsuit.
They also provide additional insulation because they prevent the flow of water between the diver’s skin and the neoprene, which results in heat loss. Wetsuits should be snug fitting to minimise any water flow, and there are some that are marketed as “semi-dry suits” – these are wetsuits with a tight fitting seal around the neck, wrists and ankles and with a waterproof zip.
In addition to full body wetsuits, two or three piece diving suits may offer you more flexibility with your diving. Think of where you are likely to dive, typical conditions and what you are used to or prefer before deciding.
The water temperature in the Costa Brava falls throughout the winter until bottoming out at around 13 degrees C by March, but I wear a 7mm ScubaPro semi-dry that sees me throughout the year. The main trick is to have decent gloves and boots – 5mm renders your hands pretty useless but I prefer that to the pain of thawing my hands after a cold dive.
Wetsuits are commonly found in 2mm, 3mm, 5mm and 7mm thicknesses – in fact after about 8mm the neoprene simply becomes too constricting to wear – think Michelin Man rather than scuba diver – but your choice of wetsuit for the Costa Brava will mainly depend on how frequently you will dive in the off season.
The temperature starts to rise with the arrival of spring so that by summer a 5mm wetsuit will be fine – the surface temperature is usually 22 or 23 degrees C. Dive centres can provide you with a wetsuit and other equipment if necessary, although they only seem to stock men’s wetsuits.