Blowing agents of the tetrazoles and their derivatives

In a process for the production of cellular products which comprises incorporating a blowing agent into rubber or a synthetic polymer and then heating to activate the blowing agent, the improvement which comprises using as the blowing agent tetrazole compounds represented by the formulae:

• ##STR5## where:
• R and R.sub.1 are the same or different and are OH, COOH, SO.sub.3 H, NO.sub.2, halogen and NR.sub.4 R.sub.5 wherein R.sub.4 and R.sub.5 are each H or C.sub.1 -C.sub.4 alkyl or R and R.sub.1 are phenyl, benzyl, or phenethyl substituted or substituted by 1 to 3 halogens, OH, NO.sub.2, COOH and NR.sub.4 R.sub.5 wherein R.sub.4 and R.sub.5 are as defined above, R.sub.2 is H, OH, COOH, SO.sub.3 H, NO.sub.2, halogen or NR.sub.4 R.sub.5 wherein R.sub.4 and R.sub.5 are as defined above, C.sub.1 to C.sub.6 alkyl, C.sub.3 to C.sub.6 cycloalkyl or C.sub.2 to C.sub.6 alkenyl, unsubstituted or substituted by C.sub.1 to C.sub.6 alkyl, OH, COOH, SO.sub.3 H, NO.sub.2, halogen or NR.sub.4 R.sub.5 wherein R.sub.4 and R.sub.5 are as defined above or R.sub.2 is phenyl, benzyl or phenethyl unsubstituted or substituted by 1 to 3 halogens, OH, NO.sub.2 or NR.sub.4 R.sub.5, wherein R.sub.4 and R.sub.5 are as defined above, C.sub.1 to C.sub.4 alkyl and esters or amides of lower carboxylic acids;
• M is Ca, Cu, Zn, Mn, Fe, Co, Ni or Ba and Z is a univalent inorganic or organic group which binds to or forms a salt with M.