Crushed vs Compressed Foam

Bob Stinton VP Engineering
Diving Unlimited International
1148 Delevan Dr
San Diego CA 92102 USA
ABSTRACT The success of Diving Unlimited International’s (DUI’s) Crushed Foam CF200 suits has spawned a number of imitations. With the advent of these imitations and their confusing marketing claims, the confusion has grown to the point that it is self perpetuating. Poorly researched articles have just added more spin to the confusion. The objective of this paper is to provide an overview of what DUI’s patented crushed foam is, and how its development came about. It is not that these imitations do not work to some degree. It is that these suits attempt to ride on the success of DUI’s CF200 series suits. In many cases, the purchaser of one of these imitations expects more from the suit than it is capable of providing. The poor performance of these suits not only blemishes the imitation’s reputation but the reputation of DUI’s CF200 series suits because the customer is not aware of the real differences. HISTORIC PERSPECTIVE The development of Compressed Foam (CF) suits stemmed from DUI’s effort to develop a material that would overcome the shortcomings of the available drysuits at the time. The most common material in use for making drysuit, then and now, is closed-cell neoprene foam a.k.a. wetsuit material. The second and less common materials used then were rubber- coated fabrics or sheet rubber. At the time, durability was a common problem in all these materials. DUI’s goal was to develop a durable material that would provide little intrinsic insulation and buoyancy and these properties would not change with depth. Additionally the material had to have some stretch to facilitate a closer fit and reduced bulk.drysuit science crushed vs compressed figure 1 Drysuits made of wetsuit material (close-cell foam) exhibited three primary problems.
  • The intrinsic insulation of foam is directly proportional to its thickness. As the diver descends the thickness and insulation of the foam decreases. At a depth of 33 feet, (Fig- 1) approximately 30% of the foams approximately 30% of the foams thickness and insulation is lost. (Penzias, pg 604)
  • The intrinsic buoyancy of the foam also experiences major changes with depth. At the depth of 33 feet, (Fig-2) approximately 50% of the buoyancy of the foam is lost. If the diver needs 20 lbs of lead to compensate for the buoyancy of the foam at the surface, by the time they reach 33 feet of depth they must compensate for approximately 10 lbs loss of buoyancy. (Penzias, pg 604)
drysuit science crushed vs compressed figure 2
  • Two factors cause the foam’s cell wall breakdown resulting in pinhole leaks: The cycle of compression and re-expansion with each dive and activities that pinching the material, such as when the diver is on their knees.
Drysuits made from rubber-coated textiles, or sheet rubbers are shell drysuits. There are two main advantages of the shell drysuits:
  • There is only a little change in insulation or buoyancy with depth. (Fig-3). Wattenbarger compared a foam drysuit vs. a shell drysuit with both suits utilizing the same undergarment. The foam suit effectively has more insulation near the surface, however this diver must utilize more lead to compensate for suits additional buoyancy. This advantage however is quickly lost with depth. (Fig-3) (Wattenbarger, pg 101-116).
  • The diver in the shell drysuit, however, can double up on the insulation and effectively archive the same level of insulation as the diver with the foam drysuit. The advantage the shell drysuit diver has over the foam drysuit diver is the insulation and buoyancy does change with depth. Also the diver can vary the amount of insulation worn in combination with the suits depending on the dive time and temperature profile. drysuit science crushed vs compressed figure 3
The down side of these rubber shell suits was that the materials commonly used did not have any real stretch. The lack of stretch requires that the suits need to fit very loosely to allow for a full range of motion. The rubber-coated fabrics that did stretch developed pinhole leaks with repeated stretching. An additional disadvantage of these suits was that the outer rubber surface, which is the part of the suit that maintains the diver dry, was subject to cuts and abrasion. DEVELOPMENT OF THE CF PROCESS DUI undertook the development of a new drysuit material, in part to respond to the U.S. Navy’s Diver Thermal Protection System Program. The Navy’s program required a shell drysuit that was both durable and swimmable. One of the lines of the investigation that DUI undertook was to look at the advantage of permanently compressed foam. Why permanently compressed foam? DUI’s experiences, with the impact of saturation diving on closed-cell foams provide the lead need. The challenge was to find a method that would permanently compress the foam without damaging its cell structure, which is the case with the foams used, in hot water suits, in saturation diving conditions. (Penzias, pg 605-610) These insights lead to a series of experiments. The experiments involved four major factors: compression rate, decompression rate, gas mix and exposure, and temperature profiles. The key to the process was to get the cells in the foam to not only compress, but to completely off-gas during the process. drysuit science crushed vs compressed figure 4The result of this effort was a process by which foam laminated with nylon on two sides (Fig-4) could be processed in such a manner to convert the closed cell structure into a stretchable membrane (Fig-5.) Figure-4 is a 4-mm foam laminate before processing and Figure-5 post processing with only 0.5-mm membrane remaining. The Navy Clothing and Textile Research Facility’s analysis of this material concluded that it was a new class of material. (Audet) Based on this analysis the US Patent Office issued two US Patents: 4,882,785 Underwater Diver’s Dry Suit Having A Permanently Compressed Cellular Layer 4,778,643 Method of Treating An Underwater Diver’s Suit These patented processes culminated in the development the CF200 material and the CF200 series suit. IMITATIONS The success of the CF200 series suits has resulted in a series of imitations. The imitations utilize thin neoprene foam and plays on words, to imply that compression or crushing is used in their manufacture. This has even spread to the foam manufacturers. The Yamamota Corporation produces Type 88 Hyper-Compressed foam, which in reality has a density of 13.4 lb/ft3 and a very small cell structure. (Yamamoto) The foam rubber used in wet suits typically range in densities from 10-15 lb/ ft3. drysuit science crushed vs compressed figure 5The reality is that the diver is purchasing closed-cell foam suits, where the thickness of the foam has been reduced. For example the foam thickness has been reduce from 6-mm to 3-mm. Though these thin foam suits do have some advantage in that they function more like shell drysuits with less intrinsic insulation and less buoyancy changes with depth. However, the cell structure of these suits will breakdown with repeated use. WHAT THE IMITATORS FORGOT The imitators have forgotten that if you compress a sheet of 6-mm foam to a thickness of 3-mm or smaller, the weight of the sheet of rubber would not change. The density of the foam would change, for example, from 10 to 20 lb/ft3 or greater. The weight of this compressed 3-mm suit would be equal to that of a 6-mm suit. For comparative purposes neoprene rubber compounds, that are not foams, have specific gravities in the range of 1.45, which relates to a density in the range of 90 lb/ft3. (Penzias, pg 492) Also, if one where to examine the exposed edges of the material under magnification, the cell structure of the foam is still visible. An informed purchaser can detect these simple differences. CONCLUSION DUI and Abyss are the only manufacturers of suits made with foam in which the cell structure has been permanently removed via compressed or crushed. The CF200 or crushed foam material developed and patented by DUI in 1985 is sill a unique and durable suit material used as a benchmark by many. One can always measure one’s success by the number of imitators. The diver with the imitation 2, 3 or 4 mm suit gains some incremental advantage in the form of reduced buoyancy changes with changes in depth. However these imitations are still subject to pinholing and other durability issue present in all foam suits. One cannot simply expect a suit perform at a high level by attaching comparable name. BIBLIOGRAPY
Audet, N. Navy Clothing and Textile Research Facility, personal communications Penzias Walter; Goodman, Man Beneath the Sea a Review of Underwater Ocean Engineering, Wiley-International, NY 1973 Wattenbarger J. F; Breckenridge, Dry Suit Insulation Characteristics Under Hyperbaric Conditions, ASME Publication OED Vol. 6.Hyperbaric Diving Systems and Thermal Protection, 1978 Yamamoto: Physical Properties Comparison Table, 1999