Trigonox® 44B is an acetyl acetone peroxide formulation for the curing of unsaturated polyester resins in the presence of a cobalt accelerator at room and elevated temperatures. With the curing system Trigonox® 44B/cobalt accelerator a much faster speed of cure may be achieved than with curing systems based on a MEKP plus cobalt accelerator, at room and elevated temperatures. Normally the gel times with Trigonox® 44B are comparable to those with Butanox M-50. Trigonox® 44B is particularly suitable in those applications where a fast mold-turnover is required, e.g. for the cold press molding or resin injection molding techniques. The system Trigonox® 44B/cobalt accelerator will give a higher peak exotherm than a standard MEKP/cobalt accelerator system. Due to this fact, is it recommendable to avoid the production of too thick laminates in one operation. At low temperatures a reasonable speed of cure is still obtained when Trigonox® 44B is used in combination with large amounts of cobalt accelerator possibly in combination with N,N Dimethylaniline as promotor.