Considerable progress has been made in column technology over the last five years.The advent of the monolithic columns in 2000 triggered an intense research effort among manufactuers of conventional columns, packed with fine particles.This effort led first to the manufacturing of sub-2 μm particles, then to that of a series of superficially porous or shell particles with sizes of 5, 2.6 and 1.7 μm.While the former particles are fully porous, the latter are made of a solid core surrounded by a layer of a porous material 0.25 to 0.5 μm thick, so far made of fused silica.Columns packed with these shell particles are far more efficient than those packed with fully porous particles, providing unexpected HETP curves, with much lower A terms and lower B terms than do the columns packed with fully porous particles.With these new columns, the same separations can be achieved in a markedly shorter time or, alternately, more efficient separations be performed in the same time as with columns packed of conventional fully porous particles.However, because the permeability of packed beds decreases as the square of the particle diameter while the optimum velocity of the mobile phase increases as the reverse of this diameter, the required pressure at the column entrance has now become very large.A stream of liquid percolating under the stress of a high pressure gradient generates by its friction against the bed an important amount of heat, causing the formation of significant radial and axial temperature gradients across the column.