Membrane Vs Neoprene
Membrane drysuits are very light weight but have very little insulation by themselves so they have to be paired with an undersuit. If you are diving in colder waters you will require a thicker undersuit to trap more insulating air next to your body. Membrane drysuits are easier to repair because of their simple construction but can be more vulnerable to damage because they are very thin.
Neoprene drysuits have their own thermal properties, keeping you warm even without an undersuit. Due to the thicker material the effect of suit squeeze is minimised, reducing any pinching. Neoprene drysuits can withstand more abuse because of their thicker materials but can feel more cumbersome.
Front Vs. Rear Entry
Drysuits are built with gender specific measurements and have two common entry types; Front & Rear Entry. Front Entry drysuits have a long diagonal zip from one shoulder to the opposing hip. Front Entry suits allow the diver to put the suit on and take the suit off by them self without any help. Rear Entry suits have a long zip along the back of the shoulders and can be easier to put on and take off but a buddy is needed to do and undo the zip.
Boots Vs. Socks
The feet on drysuits have two variants; Boots or Socks. Boots are fitted that match your shoe size allowing for thick undersuit socks. Boots are hard wearing and go straight into your fins as a wetsuit boot will. Most Boots have fin retaining notches on the heel to stop the fin strap slipping off during the dive. Socks are more flexible and can fit a wider range of shoe sizes, they do however require a separate rock boot
to be worn to use fins and prevent damage.
Shoulder Vs. Cuff Dumps
All drysuits will have an Inlet Valve similar to your BCD and a Dump Valve on the left arm. As you descend you add air to control your buoyancy and relieve any squeeze due to pressure, this air needs to be expelled as you ascend to control your rate of ascent. Automatic Shoulder Dumps can be set to be fully open/closed or somewhere inbetween during a dive so it will release excess air. Cuff Dumps are simpler one-way valves on the left forearm and work by releasing air when the arm is lifted above the head. Both types of Dump will let a small amount of water into the suit with heavy use and surface work but only the Shoulder dump can be closed completely.
Latex Vs. Neoprene Vs. Silicone Seals
All drysuits have two types of Seals; Cuff/Wrist Seals and a Neck Seal. Seals can be made from one of 3 materials; Latex, Neoprene or Silicone. Latex is a thin and stretchy material that creates a tight effective seal that stretches slowly over time to the correct size. Neoprene is a softer material that can put up with more abuse and can be more comfortable but needs to be fitted correctly. Silicone is the newest type of seal which is similar to latex but more stretchy and robust. Silicone Seals however will not stick to any glues and such require a hard plastic halo system to be fitted to the suit so that Silicone Seals can be used.
Other parts to look for on a drysuit are; Telescopic Bodies that overlap over the abdomen to allow for taller or shorter divers to fit in the same size suit comfortably. Reinforced Knee Pads protect the knee from wearing on rough substrates. Thigh Pockets allow you to keep spare masks, tools or emergency equipment close to hand and easily accessible. Braces hold the drysuit in a comfortable position during the dive and hold the drysuit up when walking around the dive-site with the top half down.