FRTP의 경우 Coupling agent로 표면처리한 fiberglass의 함량은 30 %일 때 가장 좋은 강도를 나타내고 있으며 fiberglass에 있어서 알칼리성분이 적어야 좋은 물성을 나타낸다는 사실을 확인했다.
Fiberglass를 표면처리할 때 coupling agent의 농도는 LDPE와 HDPE는 0.01 %, PP는 0.05 %일 때 물성이 좋음을 알았다.
또한 FRTP에 있어 HDPE는 fiberglass를 표면처리하지 않고 사용했을 경우보다 오히려 fiberglass를 넣지 않았을 때가 물성이 좋았다. 접착메카니즘에 관하여는 coupling agent가 fiberglass에 흡착된 후에 수지와 수소결합 혹은 -OH결합을 형성하여 접착강도가 매우 좋아지는 것으로 해석되며 이러한 현상이 적외선 스펙트럼에 의하여 확인되었다.

The tensile strength of fiberglass reinforced thermoplastics reached the maximum when the content of fiberglass treated by coupling agent was 30 %. The physical properties were improved as the alkali content in fiberglass was decreased. For the surface treatment of fiberglass the optimum amount of coupling agent turned out to be 0.01 % for both low-density polyethylene and high-density polyethylene and 0.05 % for polypropylene. It was also noticed that the addition of fiberglass caused unfavorable effects on physical properties when the surface was not treated by coupling agent. Concerning the mechanism of adhesion, the coupling agent was understood to adsorb on fiberglass, then form the hydrogen bond or hydroxyl bond with resins, and there by enhance the adhesive strength. This argument was supported by the Infra-red spectrum.