Unique 
thermoplastic monofilament fibers and yarns that exhibit heretofore unattained physical properties are provided. Such fibers are basically manufactured through the 
extrusion of 
thermoplastic resins that include a certain class of nucleating agent therein, and are able to be drawn at high ratios with such nucleating agents present that the tenacity and modulus strength are much higher than any other previously produced 
thermoplastic fibers, particularly those that also simultaneously exhibit extremely 
low shrinkage rates. Thus, such fibers require the presence of certain compounds that quickly and effectively provide rigidity to the target thermoplastic (for example, 
polypropylene), particularly after heat-setting. Generally, these compounds include any structure that nucleates 
polymer crystals within the target thermoplastic after 
exposure to sufficient heat to melt the initial pelletized 
polymer and allowing such an oriented 
polymer to cool. The compounds must nucleate 
polymer crystals at a higher temperature than the target thermoplastic without the nucleating agent during cooling. In such a manner, the "rigidifying" nucleator compounds provide 
nucleation sites for thermoplastic 
crystal growth. The preferred "rigidifying" compounds include 
dibenzylidene sorbitol based compounds, as well as less preferred compounds, such as [2.2.1]
heptane-bicyclodicarboxylic acid, otherwise known as HPN-68, 
sodium benzoate, certain 
sodium and 
lithium phosphate salts [such as 
sodium 2,2'-
methylene-bis-(4,6-di-tert-butylphenyl)
phosphate, otherwise known as NA-11]. Specific methods of manufacture of such inventive thermoplastic fibers, as well as fabric articles made therefrom, are also encompassed within this invention.