A chemical blowing agent for foaming a thermoplastic polymer precursor, for example PVC plastisol or a polymer resin in an extrusion process, said chemical blowing agent comprising a functionalized particulate bicarbonate, wherein said functionalized particulate bicarbonate contains at least one functionalization additive, and wherein said functionalization additive in the functionalized particulate bicarbonate comprises a polyoxyalkylene additive selected from the group consisting of: a polyethylene oxide PEO polymer, a polyethylene glycol PEG polymer, a polypropylene oxide PPO polymer, a polypropylene glycol PPG polymer, a co-polymer or block polymer which is made with at least one monomer of propylene oxide or propylene glycol, a co-polymer or block polymer which is made with at least one monomer of ethylene oxide or ethylene glycol, a polyethylene glycol / polypropylene glycol PEG/PPG block co-polymer, such as the PEG/PPG/PEG triblock polymer, or any derivatives thereof meaning wherein any of these polymers may be chemically functionalized or not, salts thereof, and any combination of two or more thereof, wherein the functionalized particulate bicarbonate comprises at least 50% by weight and less than 100% by weight of the bicarbonate component, and from 50% or less to 0.02% by weight of at least one of said functionalization additive, and wherein the particles of the functionalized particulate bicarbonate have a particle size distribution of D 50, as determined according to the method described in the description, of more than 1 μm and at most 250 μm. said chemical blowing agent comprising a functionalized particulate bicarbonate, wherein said functionalized particulate bicarbonate contains at least one functionalization additive, and wherein said functionalization additive in the functionalized particulate bicarbonate comprises a polyoxyalkylene additive selected from the group consisting of: a polyethylene oxide PEO polymer, a polyethylene glycol PEG polymer, a polypropylene oxide PPO polymer, a polypropylene glycol PPG polymer, a co-polymer or block polymer which is made with at least one monomer of propylene oxide or propylene glycol, a co-polymer or block polymer which is made with at least one monomer of ethylene oxide or ethylene glycol, a polyethylene glycol / polypropylene glycol PEG/PPG block co-polymer, such as the PEG/PPG/PEG triblock polymer, or any derivatives thereof meaning wherein any of these polymers may be chemically functionalized or not, salts thereof, and any combination of two or more thereof, wherein the functionalized particulate bicarbonate comprises at least 50% by weight and less than 100% by weight of the bicarbonate component, and from 50% or less to 0.02% by weight of at least one of said functionalization additive, and wherein the particles of the functionalized particulate bicarbonate have a particle size distribution of D 50, as determined according to the method described in the description, of more than 1 μm and at most 250 μm. a polyethylene oxide PEO polymer, a polyethylene glycol PEG polymer, a polypropylene oxide PPO polymer, a polypropylene glycol PPG polymer, a co-polymer or block polymer which is made with at least one monomer of propylene oxide or propylene glycol, a co-polymer or block polymer which is made with at least one monomer of ethylene oxide or ethylene glycol, a polyethylene glycol / polypropylene glycol PEG/PPG block co-polymer, such as the PEG/PPG/PEG triblock polymer, or any derivatives thereof meaning wherein any of these polymers may be chemically functionalized or not, salts thereof, and any combination of two or more thereof, wherein the functionalized particulate bicarbonate comprises at least 50% by weight and less than 100% by weight of the bicarbonate component, and from 50% or less to 0.02% by weight of at least one of said functionalization additive, and wherein the particles of the functionalized particulate bicarbonate have a particle size distribution of D 50, as determined according to the method described in the description, of more than 1 μm and at most 250 μm.