disadvantages. The goal of the current study was to evaluate the new Clear Advantage Series II durable thermovacuum formed invisible orthodontic retainer material and compare the clinical performance of such retainer with the most standard types of retainers (convention Clear Advantage Series I thermo-vacuum formed invisible retainer, Hawley, and the fixed lingual bonded retainers). The conducted study is the first attempt to evaluate and compare the clinical performance of different retainers' types. Subjects and methods: Twenty finished fixed orthodontic patients starting the retention phase were divided into four groups. Each group consisted of five patients (3 females and 2 males), mean age ranged 18-30 years old. Members of the first group were given the new thermo-vacuum formed invisible Clear Advantage Series II durable retainer material (CII), While the second, third, and fourth groups were given standard thermo-vacuum formed invisible Clear Advantage Series I retainer material (CI), Hawley retainer (HR), and fixed lingual bonded retainers cuspid to cuspid(FR), respectively. Ten variables were applied on the twenty patients to evaluate the clinical performance of the four retainers' types, the ten variables were evaluated and judged by the operator with the patient as three nonparametric categorical descriptions: superior (+), acceptable (±), and inferior (-) properties. Results: It was found that patients were compliant with all types of retainers initially, and the compliance decreased at a much faster rate with both types of themo-vacuum formed retainers (CII and CI) than with HR and FR retainers, and patient's compliance is greater with HR and FR retainers than with CII and CI retainers. A comparison of the total variables of the clinical performance at total time intervals using chi-square showed that there was a significant difference (P<0.05) in the acceptable categorical description between CII and CI retainers and very high significant difference (P<0.001) between CII, HR, and FR retainers. Conclusion: it was found that the new thermo-vacuum formed Clear Advantage Series II durable retainer showed a combination of removable, comfortable, aesthetic, better speech, superior retention, relatively not producing bad taste and odor, hygienic, least soft tissue irritability, superior construction and chair-side time, and durable, it will be more favorable clinical performance appliance to both the patient and the orthodontist.