WET SUITS 



281 



Table 34 

 MICROBALLOON/PVC PLASTISOL THERMAL CHARACTERISTICS 



*The volume of closely packed uniform spheres in space is 53 percent. The 

 volume of closely packed microballoons in space is approximately 69 percent. 



Microballoons were first considered because, in the loosely packed condition and without a 

 binder material, the thermal conductivity is close to that of cellular neoprene used for standard 

 wet suits (Tables 35 and 36). This information is given in the manufacturer's specifications 

 and thermal-conductivity measurements were not made during this program to verify the manu- 

 facturer's data. 



Table 35 

 MICROBALLOON PROPERTIES [9] 



An analysis of the heat transfer across such a composite material indicates that thermal 

 short-circuiting occurs across the elastomeric material used as the binder and across the 

 glass microballoon walls. The microballoon wall materials exhibit about eight times the ther- 

 mal conductivity of PVC, which tends to offset insulation due to the voids within the micro- 

 balloons. See table 36 for comparisons of the thermal conductivities of materials. 



To make matters worse, the composite microballoon/elastomer material is very stiff com- 

 pared to the same thickness of the elastomer alone. The high bending and elongation stiffness 

 of the material makes it a poor choice for a flexible diver's suit. There is also a decrease in 

 tensile and elongation strength (Table 37). 



