Lycra is a tradename of a fabric developed by Dupont. Lycra does have a component of Nylon to it. Companies may use Lycra or Nylon Spandex or another combination of the same fabrics which they tradename such as Ultraspan as an Outer Skin to a Neoprene.
I will group Lycra and Ultraspan together since they are similar. These are considered High Stretch Outer Materials for single or double lined neoprene. In addition to being more flexible, ie Ultraspan has 24O% more flexibility than standard Nylon, Lycra and Ultraspan are also thicker and more durable as they are much thicker materials. If you look at a piece of Nylon that is used to laminate onto foam rubber to make Neoprene, it is see through. It's very thin, almost like a panty hose material, whereas Lycra or Ultraspan are opaque and could be worn as clothing. This being said there are many different kinds of Lycra/Ultraspan ie thickness or weight for example, 4oz. 6oz. 8oz. etc.. There are also many different kinds of Nylon and different material manufacturers Nylon will have different characteristics. For example, there is Nylon.. and then there is High Stretch Nylon which has 17O% the stretch of regular Nylon.. Wetsuits are complex.
Open Cell vs. Metalite vs. "Super Stretch"
Open Cell has almost unlimited stretch.. If there was no material on one side of the foam, and both were Open Cell, the material would stretch until it ripped. Open Cell is very comfy, warm, flexible, but requires water or lube to put on the suit.
Metalite is supposed to make an open cell suit eaisly slide on.. but this skin, does restrict slightly the flexibility, is not as warm as open cell and has an annoying tendency to peel off over time.
Super Stretch, or XTEND.. matches the flexibility of a High Stretch Outer Material ie @27O% the stretch of Nylon. It is thinner as it does not need to have the resistance to Barnacles etc.. as such it is actually more flexible than the outer skin. An XTEND/XTEND suit would be extremely flexible but not very resistant to abrasion.. good for example for Triatheletes..
What would I get?
Up to 2.5mm I would go with XTEND
2.5mm -3.5mm I would go with any of the three
5mm and up.. Open Cell.
Hope that helps.