The hypothesis that in folding of a newly synthesised or renaturing biopolymer, a protein or RNA quickly collapses into condensed structures characterised by a high degree of secondary structure. One of these may be the native conformation (the others are “kinetic traps”), but significant energy barriers isolate these forms. Kinetic partitioning is the hypothetical basis of recognition of proteins by molecular chaperones: quickly after synthesis, a cytosolic protein achieves its native conformation and thus avoids binding to the chaperone, while other proteins, e.g. those with leader sequences, much more slowly fold into native structures, which affords the chaperone the opportunity to bind them.