Methyl ethyl ketone peroxide
Methyl ethyl ketone peroxide (MEKP) is an organic peroxide
Organic peroxide
Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...

, a high explosive similar to acetone peroxide
Acetone peroxide
Acetone peroxide is an organic peroxide and a primary high explosive. It takes the form of a white crystalline powder with a distinctive bleach-like odor....

. MEKP is a colorless, oily liquid whereas acetone peroxide is a white powder at STP
Standard conditions for temperature and pressure
Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...

; MEKP is slightly less sensitive to shock and temperature, and more stable in storage.

Dilute solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

s of 30 to 60% MEKP are used in industry and by hobbyists as the catalyst which initiates the polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 of polyester resin
Polyester resin
Polyester resins are unsaturated resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Polyester resins are used in sheet moulding compound, bulk moulding compound and the toner of laser printers...

s used in glass-reinforced plastic
Glass-reinforced plastic
Fiberglass , is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK ....

, and casting.