Associates with aggregated proteins, together with IbpA, to stabilize and protect them from irreversible denaturation and extensive proteolysis during heat shock and oxidative stress. Aggregated proteins bound to the IbpAB complex are more efficiently refolded and reactivated by the ATP-dependent chaperone systems ClpB and DnaK/DnaJ/GrpE. Its activity is ATP-independent. Thermostable up to 50 degrees Celsius. Homodimer. Forms homomultimers of about 100-150 subunits at optimal growth temperatures. Conformation changes to oligomers at high temperatures or high ionic concentrations. The decrease in size of the multimers is accompanied by an increase in chaperone activity. By heat shock. The N- and C-terminal flexible termini are involved in oligomerization and in the binding of non-native substrate proteins, and are essential for chaperone activity. Belongs to the small heat shock protein (HSP20) family. Extended N-terminus.