Nowadays, Polyester fibers are the most important man-made Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Fabrics woven or knitted from polyester thread or yarn are used extensively in apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets and upholstered furniture. Industrial polyester fibers, yarns and ropes are used in tyre reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high-energy absorption. Polyester fiber is used as cushioning and insulating material in pillows, comforters and upholstery padding. Polyester fiber is one of the best choices for clothing, furniture, carpet, floor covering, home textile, because of its magnificent and unique features like : elegance, lightness, excellent shape and look and suitable price. However, this fiber has some weak points which should be modified by physical or chemical methods. Previously acrylic fiber was the most important fiber used for producing high-bulk yarns, but this fiber is more expensive than polyester and is very sensitive to heat and its spinning is difficult, because of using DMF as a solvent for the process of spinning. DMF damages environment. Most of high-bulk yarns which are now available are in the form of staple. High-bulk polyester continuous filament yarns have advantages like: high speed production by omitting lengthy process of producing staple yarns, low price raw materials, low product expense, low amortization and simple process. In this project, by means of physical modifications on polyester filament yarn, the possibility of producing high-bulk yarn from polyester filament yarn is studied and its important features like: mechanical properties, bulk and heat resistance are measured. Moreover, the new yarn was compared with some other yarns like acrylic staple high bulk yarn and fancy boucle yarn. In order to do this, Partially oriented yarn(POY) polyester was stretched with different drawing ratios from1.2 to 2.2 with interval of 0.2 at different temperatures 25°c (room temperature) and 80°c (Tg of polyester) as shrinking part .Fully drawn yarn(FDY) polyester was used as a non-shrink part. The shrink and non shrink yarns were combined by means of an air-jet. The best blending ratio for optimum bulk was found to be 50-50 from each part. The bulk of some of the produced high-bulk yarns is 11 times higher than that the yarns before relaxation. As a result, the heat resistance of the high-bulk yarns increase considerably. The shape of high-bulked yarn produced in this way showed a high degree of similarity with boucle fancy yarns. The production of fancy yarn in this way is much easier, moreover the cost of production is much less. This process can be a suitable substitution for acrylic high-bulk yarns.