GT Products has re-formulated our mid-grade mold making system. The only difference that will be noticeable is simply the color of the catalyst. The regular speed catalyst will now be orange and the alternate fast catalyst will be green. GT 6142 still has impeccable strength and will continue to be one of our most reliable and most popular materials. Although this material is classified as a mid-grade system, the precise detail that can be obtained, the long mold life, and the strength you will notice are remarkable for the price. Do not hesitate to give it a shot. If you have any questions then please contact us anytime.