239.367B Figure 10-2.—Basic weaves. are  many,  many  different  types  of  fabrics,  or cloth.  When  we  say  cloth,  we  mean  any  textile material  over  12  inches  wide  from  selvage  to selvage. The  construction  of  cloth  is  determined  by many  factors,  such  as  tightness  of  yarn  twist, number of threads per inch, porosity of the yarns, and the type of weave used in its formation. The weave is one of the most important factors. The two  basic  weaves  are  plain  and  twill  (as  shown in  figure  10-2).  The  plain  weave  is  the  simplest method  of  weaving  and  gives  the  smoothest surface  of  the  fabric.  It  consists  of  the  filling threads passing over one warp thread and under the next warp thread. The twill weave is a more complicated  weave  in  which  the  filling  threads pass over and under more than one warp thread, thereby producing a surface on the fabric that is generally  recognized  as  a  diagonal  pattern. Cotton Cotton is a natural plant fiber, usually white. The  fibers  or  “staples”  are  between  3/8  and  2 inches  in  length.  Chemically,  it  is  almost  pure cellulose.  Cotton  fabrics,  webbing,  and  tapes absorb  water  readily  unless  treated.  They  dry more  slowly  than  the  synthetic  fabrics  and  are more  susceptible  to  mildew  and  fungus  growth. One should never ignore the presence of mildew because it seriously affects the tensile strength of cotton  and  other  fabrics.  Heat  is  less  damaging to  cotton  than  to  the  synthetics.  Insect  damage should,  however,  always  be  considered  because cotton  is  a  food  for  certain  cellulose-eating  insects, and  cotton  makes  good  nesting  or  cocoon- spinning  material  for  rodents  and  insects. Nylon This is a synthetic fiber of extreme toughness and elasticity. It absorbs very little water, dries quickly,  is  mildewproof,  and  is  not  affected  by most ordinary oils, greases, or cleaning fluids. It is also mothproof. It is sensitive to some chemical fumes, excessive heat, and direct rays of sunlight. Nylon melts and drips when it is subjected to fire. This  characteristic  requires  that  precautions  be taken  when  nylon  is  worn  where  there  is  a  risk of  fire.  Melted  nylon  on  the  skin  can  cause  the most  serious  of  burns. NOMEX Fabric NOMEX  is  the  trade  name  for  a  fabric  that is used in the construction of flight suits. NOMEX fabric  is  a  high-temperature  resistant  and inherently flame-retardant synthetic fabric. This fabric  has  no  melt  point  or  drip  characteristics when it is subjected to fire. NOMEX material is light in weight, does not support combustion, but begins  to  char  at  700°  to  800  °F.  The  fabric, similar to nylon, is abrasion resistant, and is also nonabsorbent. Duck This  is  a  comparatively  firm,  coarse,  plain- weave, cotton fabric with weight per square yard from  6  to  50  ounces.  Duck  is  frequently  called canvas. It is primarily used in the construction of protective  covers  because  of  its  durability  and wearing  characteristics. Rubber   and   rubberized   fabrics   are   used in   the   manufacture   of   exposure   suits   and flotation  equipment  because  they  are  water- tight.   Rubberized   materials   are   susceptible to  deterioration  if  subjected  to  heat  and mildew.  Foam  rubber  is  thick  and  resilient  and is  used  for  padding  in  upholstery  and  aircraft crash  pads. 10-3