Nanometer control over the porous shell thickness of sub-2-μm-shell particles is investigated. Three seeded growth mesoporous thin shell particles for HPLC were prepared, with 0.05μm (or 50nm) porous shell layers: particle sizes 1.5μm (solid core diameters 1.4μm), 1.7μm (solid core diameter 1.6μm), 1.9μm (solid core diameter 1.8μm) and compared with a fourth 1.7μm particle (solid core diameter 1.4μm) surrounded by 0.15μm (or 150nm) porous shell thickness. The thin shell particles were functionalised using a mono-functional octadecyldimethylchlorosilane ligand (C20H43SiCl) under optimised reflux conditions and packed in-house in narrow bore columns (2.1 I.D.×50mm) denoted as TS1.5-50-C18, TS1.7-50-C18, and TS1.9-50-C18 respectively. The synthesised thin shell particles and bonded materials were comprehensively characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential, BET analysis, elemental analysis (CHN), thermogravimetric analysis (TGA) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Experimental data from inverse size exclusion chromatography (ISEC) was used to measure external, internal and total column porosities. Five probe analytes (uracil, naphthalene, acetophenone, benzene and toluene) were chosen for the chromatographic performance analysis of these columns. Column evaluation and measurements of height equivalent to a theoretical plate (HETP) data were performed on naphthalene using 55% acetonitile in water. The retention coefficients for the thin shell particles (TS1.9-50-C18, TS1.7-50-C18, TS1.5-50-C18) were in the range 1.26-1.35 and 5.6 for the core-shell particle (EiS1.7-150-C18). The minimum reduced plate heights range from 3.89 to 4.26 for the thin shell particles and 2.03 for the core-shell particle.