We study random sequential adsorption of flexible chains onto a two-dimensional lattice by computer Monte Carlo simulations. The flexibility of chains is controlled by the temperature of the solution via the Boltzmann factor. We investigate the percolation threshold in the system as a function of chain length and temperature. Several temperature regimes are identified, and respective characteristic types of behavior of the system are discussed. Especially, nonmonotonicity of percolation threshold is observed-there appears a characteristic temperature unique for all chain lengths for which the percolation threshold attains its minimum.