Method for producing expanded and cured polyester resin

A foamable and curable polyester composition consisting essentially of, all parts being by weight:

• (a) 100 parts liquid unsaturated polyester resin,
• (b) 2.7-32 millimoles mono-substituted sulfonyl hydrazide blowing agent for the resin having the structural formula RSO.sub.2 NHNH.sub.2, wherein R is C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.6 cycloalkyl, C.sub.7 -C.sub.10 aralkyl, phenyl, naphthyl or phenyl substituted with halogen, C.sub.1 -C.sub.12 alkyl or C.sub.1-C.sub.12 alkoxy,
• (c) 0.001-2 parts organic metal salt primary promoter for the organic peroxide or organic hydroperoxide cure of the resin wherein the metal is selected from copper and vanadium,
• (d) 0-0.4 part organic metal salt secondary promoter for the organic peroxide or organic hydroperoxide cure of the resin, wherein the metal is selected from cadmium, calcium, chromium, cobalt, iron, lead, lithium, manganese, nickel, tin and zirconium,
• (e) 0-2 parts surface active agent,
• (f) 0-250 parts filler,
• (g) 0.5-2.5 parts organic peroxide or organic hydroperoxide per 100 parts (a) plus (f);
• provided that if the amount of (d) is zero the amount of (c) is at least 0.01 part.