A lining is an extra insulating layer on the inside of a wetsuit, mainly found on mid-range to premium suits. The lining materials used will still be stretchy and lightweight, as well as water-repellent and fast drying, so you don't end up with heavy, soggy fleece against your skin.

With advancing wetsuit technology, different brands are coming up with their own lightweight, super insulating linings to better retain heat without the need for thicker neoprene. This is a great feature to have on a wetsuit because thinner neoprene equals more stretch, and if you're surfing in cold water, it will really make a difference.

When it's cold, a lining is a great addition to your suit, adding more warmth without having to sacrifice the flexibility of the wetsuit. However, that doesn't mean you'll always want a lining if it's available to you. Though these materials are getting lighter and more flexible, for warm weather surfing you just won't need one, and for competitions or the more active watersports, the flexibility should be valued over the extra insulation, as you'll keep yourself warm enough just moving.

If you do opt for a lining, it's worth noting that the area covered by it on each wetsuit will vary. Essentially the more you're willing to pay, the more coverage you'll get, and if you're regularly surfing winter swells, it's worth the upgrade. Some wetsuits won't have a lining at all, such as entry level or summer suits, whereas some wetsuits will be fully lined (1), some just the legs and torso (2) and some may just have a single panel on the front (3), to better protect your core.