Insulation strategies for drysuit divers

By Dick Long The Basics: Let’s start with a few basic concepts: The drysuit only keeps you dry. It does not keep you warm. The DiveWear insulation keeps you warm. The amount of insulation you require will be determined more by your exercise rate than by the water temperature you are diving in. After all, the muscles of the body are the heat engines of the body. The amount of heat produced by a person who is working hard may be as much as seven times greater than someone at rest. Think of the amount of clothing you need if you are standing in the cold outdoors in the wintertime, or if you are chopping wood. If you are standing still, you need all the insulation you can get. If you are walking, it’s a little better. And if you are chopping wood, you probably have to take your jacket off. Same person, same air temperature, different exercise rate. Underwater photographers and divers using scooters have the same problem. Even in relatively warm water, they get cold. The circulatory system is the heat distribution system of the body. Therefore it is critically important to ensure good blood circulation as well as thermal insulation. Anything that we do that reduces blood flow is going to reduce heat flow. A tight wrist seal will reduce the blood flow to the hands which also correspondingly reduces the heat flow to the hands. That is particularly important because the hands have the largest surface-to-mass ratio of all body parts by far, and as a result, they are usually the first to get cold. Unfortunately, they also usually have the least amount of insulation on them. Walking on the ground stimulates blood flow because your blood has weight in air. When one goes underwater, swimming does not stimulate blood flow because your feet do not impact on the ground. Your blood has no weight because “water in water is water.” Therefore it’s very important that whatever you wear on your feet not be too tight. You should wear something that fits like bedroom slippers not running shoes. A drysuit needs to fit loosely enough to allow the maximum amount of underwear you will ever wear underneath it without restricting your movements or breathing. It also needs to fit closely enough for maximum comfort. One needs to check the fit of the drysuit with the maximum amount of underwear you will ever use and check it for the range of motion it will allow. You should do the same range of motion exercise for the DiveWear insulation as ill-fitting insulation may cause restriction often attributed to the drysuit. While most divers can use the same dive computers and/or dive tables safely, we cannot use the same insulation guidelines for keeping warm. People vary greatly in heat production, and therefore in insulation requirement, due to ethnic ancestry, body type, age, gender and more. Some people have developed large muscle masses which mean large heat engines. As a result, large people with large muscle mass need less insulation for the same exercise rate and same water temperature than smaller people with a smaller muscle mass. As we age, our circulatory systems are not as efficient as they were when we were younger. Therefore what would keep us comfortable when we were younger will no longer keep us comfortable when we are older. You can look around any large room with lots of people, and some will be wearing t-shirts and others will be wearing sweaters or sweatshirts. We are all different. All Insulation is Trapped Air/Gas All insulation known to man is trapped air or other gas. For greatest efficiency, the smaller compartment that the gas is trapped in the better. The insulation is degraded by the thermal conductivity of the insulation material. Example, heavy fibers or strong, thick fibers normally conduct much more heat than do small, lightweight fibers. The only materials suitable for modern drysuit insulation are polyester and polypropylene. Furthermore, once the diver enters the water and the water compresses against the drysuit, it sandwiches the insulation between the drysuit and the diver. Water pressure will also subject the insulation to a compression load. Whatever material the DiveWear is made of will need to resist that compression load. As a rule, the lower priced materials have fewer threads per square inch and higher loft; thus lower compression resistance. Some materials will lose as much as 70% of their insulating value while under the sort of compression experienced by the average drysuit diver. High quality materials will have more threads per square inch and are more compression resistant. You get what you pay for! DiveWear Materials: Choosing the correct material for you is not easy. Often, selecting insulation is more difficult than selecting the right drysuit. Here is a brief comparison of the materials used by DUI. Thinsulate™ Insulation Thinsulate™ Insulation is made of a polypropylene fiber that is 1/1000th the size of a human hair. Polypropylene is a modified wax. This type of insulation is the most efficient insulator known at this time (weight to warmth ratio). DUI uses 200gram and 400gram compression resistant Thinsulate™ Insulation sometimes known as Thinsulate™ Insulation Type B or Ultra. This type of Thinsulate™ Insulation is commonly used in footwear as it will retain its insulating value even under compression from someone standing on top of it. In addition, the fibers are matted together so closely that the natural resistance of wax to water prevents water from entering the insulation even if water did enter the suit. Unless there is strong pressure on the material from a serious suit squeeze, the water droplets will not touch one another and they cannot conduct heat. The body will have to heat the water in the suit, but as long as the water droplets remain trapped in the fibers and do not touch each other, they can not conduct heat away from the insulation. This characteristic makes Thinsulate™ Insulation a great choice. Fleece There are many fleeces available on the market today. Some are at a very low price. There are fleeces that do not stretch in any direction and are often used in combination with a nylon or microfiber layer for wind resistance. They will fit loosely as they do not have any stretch and you need to be able to move without restriction. Some restriction is still possible in the drysuit however, as the loose fit is compromised by the squeeze of the drysuit. There are also fleeces that stretch in one direction only. Their prices average twice that of fleece that does not stretch. This material is normally cut so it stretches horizontally which allows the diver to move much more freely when the suit is under compression. However it has no vertical stretch. Both of these types of fleece can be found in different densities, and thus will have different abilities to resist the compression of the suit. Remember, all insulation is basically trapped air/gas. The fleece used by DUI in the ActionWear™ and ThermalMax™ lines is of moderate density and is available in two thicknesses. The premium two-way stretch Polartec® material, called PowerStretch®, will cost approximately three times as much as the one-way stretch material and five times as much as the non-stretch material. However, it gives the greatest freedom of movement and has the highest density of all of the Polartec/fleece materials. Its close fit and high density mean you can use less weight than any other type of insulation of equivalent warmth. It is a great choice for hard to fit folks and smaller people who may be encumbered by the bulk of Thinsulate™ Insulation. Remember, smaller people tend to get colder faster than larger people and may need to layer with this material in colder water. Water Vapor Within minutes of closing the zipper on your suit the air inside of your suit reaches 100% humidity. The average person gives off one cup of water an hour even while at rest. That water will evaporate and migrate through the insulation to the inside of the drysuit. It will condense there because this part of the drysuit will be cold just as water vapor will accumulate on a cold window in the winter. When you take your drysuit off after your dive, you will find that the outer parts of your DiveWear and the inner parts of the drysuit are now slightly damp. This is the natural water that came out of your skin and condensed. If you are wearing a porous material such as any of the fleeces, you can look on the outside of the material and see little shiny beads of water. The first time the wind blows over it, they will evaporate creating cold air and the diver will feel it immediately. If the DiveWear has a taffeta, microfiber or a smooth wind barrier on the outside, you will not feel the cold air. Although evaporation still takes place, the air will not come through the DiveWear. Additional Factors to Consider Extended Dives / Decompression If you are going to be in the water for a long time, longer than 90 minutes, you will normally need more insulation to be comfortable than the thermal guidelines would indicate even in relatively warm water. Also, divers who will be decompressing during a dive will have higher thermal needs as much of the dive will be spent doing little or no exercise. Argon One can increase the effectiveness of the insulation of the suit by replacing the air inside the suit with argon. To do this effectively, one needs to purge the suit at least three times with argon prior to the dive. You will get up to a twenty percent increase in insulation. That twenty percent is quite noticeable. Many dive stores now fill argon bottles. SPECIAL NOTE: Do not put argon in a bottle that a breathing regulator can be attached to. There have been several instances where children have put a regulator on an argon bottle and started breathing off of it. It only takes about four breaths to render someone unconscious. Hands We have found that for most people, as the water temperature starts to go down, wetsuit gloves are simply not adequate to keep the hands warm. You need dry gloves. When you have dry gloves it is very important that the insulation be relatively loose around the fingers so it will not restrict blood flow which restricts heat flow. There are a couple of types of dry gloves you can use depending on your needs. Suit integrated gloves, called SI-5’s, are a great option for those who get very cold hands and/or have a problem with blood circulation into the extremities. This system attaches a ring permanently to the suit and eliminates the wrist seal when using the dry gloves. This provides the best blood and air circulation into the hands and is the warmest way to go. For someone diving in an environment where it is likely you could easily puncture or tear the glove, you can use the SI-Tech system which allows you to use a wrist seal and a glove at the same time. The diver must weigh the advantages of the warmer hands against the potential casualty of rupturing a glove. This decision must be dictated by the type of diving you are doing. If you accidentally puncture a glove during a dive and water starts to drip in, just hold your hand above your head. If there is a hole in the glove, a stream of bubbles will come out of it. If you hold your hand up and bubbles come out, no water can go in- keeping your hand and suit dry. Just change the glove between dives. This works well for small pinhole leaks. The Layering Strategy A drysuit diver will be faced with a wide variety of water temperatures and exercise rates. You will not want to wear the same insulation in all diving conditions. Overheating is often more dangerous than being cold. For maximum flexibility, layering is a great option. You can combine several different types of DiveWear to meet the needs of the individual diver and the particular dive. Your “set” should consist of four separate items that, when combined in different configurations, will meet most of your diving needs. Primary layer Selection should be based on your own thermal needs. Take a look at DUI’s Thermal Guidelines for help in determining what may work for you. The primary layer could be Polartec® PowerStretch® 300 (two-way stretch), Thinsulate Insulation™ 200 or Thinsulate™ Ultra 400 (400 is twice the thickness of 200.) Liner A lighter weight polyester fleece jumpsuit, such as the ActionWear™ 150, works well. You choice of liner will be affected by the primary layer as you will want to wear a two way stretch liner under the PowerStretch® material to avoid bunching. You may want something even thinner under the Thinsulate™ Insulation™ . Vest The ActionWear™ vest comes in two layers of polyester fleece material. Boots We recommend you purchase the thickest boots you will ever want to wear and use them for all occasions. The sock or turbo sole on the suits is designed to fit best when worn with thick insulation, such as Thinsulate™ Ultra 400. If you always wear the same insulation on your feet, you can ensure the best fit on the boots, and you will always be able to use the same fins comfortably. Don’t worry, we have done exhaustive research and no one has ever died of hot feet! With this combination, the diver can pick the best combination for the day’s dive depending on the water temperature and exercise rate. At what temperature and/or exercise rate you change layers is strictly up to you and your comfort level. Your body will tell you what works for you. Remember, any time you change your DiveWear, you are changing the amount of insulation you are carrying or the amount of air you are carrying which in turn changes the buoyancy of your overall system. Very soon you will learn how much weight it takes to dive with each piece. Tips on Drying and Cleaning Your DiveWear Thinsulate™ Insulation If for some reason you are diving and your DiveWear gets very wet, it doesn’t mean you have to stop diving. Get a couple of people to help wring out the DiveWear as best they can. Make sure most of the water is out of the insulation and then swing the DiveWear over your head so the water migrates to one end before wringing it out a second time. Though the DiveWear is very cold because of the evaporative cooling from swinging it in the air, it will take only a few minutes for you to warm the remaining water in it once you put it on. You will have about eighty-five percent of your original insulation, and you can continue your diving for the day. If your DiveWear begins to have a strong odor it is because your body gives off not only water but oil. The oil contains bacteria which gets inside the DiveWear and grows creating the odor. We normally treat this by washing the DiveWear in a washing machine. Fill the washing machine with water, force the DiveWear into the water, then add a cup of bleach or white vinegar and run it through at least one wash cycle. DO NOT HANG IT UP TO DRY. Lay it flat and allow it to dry naturally - not in a dryer. The bleach or vinegar will kill all the bacteria and eliminate the odor. If you wear a thin layer of polypropylene under the Thinsulate™ Insulation, this layer will absorb the oil and bacteria. You will save on the washing of your Thinsulate™ Insulation DiveWear. If saltwater gets inside your suit you can run it through a rinse cycle to get rid of the salt. You don’t have to use soap. If you use soap on Thinsulate™ Insulation you must run it through three complete wash cycles to get the soap out of the Thinsulate™ Insulation. Soap inside the material can effect its ability to repel water. Therefore it is recommended you avoid that if you can. Fleece Laundering fleece is much easier as it can be washed and dried similarly to normal clothing. You should use a small amount of soap in the washer and the low heat cycle on the dryer. Special Note: When you are on a dive boat it is recommended that you put your name on the size tag of the DiveWear to avoid mix-ups. Checking the Weight Requirement: See the Thermal Guidelines for details Thinsulate™ is a trademark of 3M