Introduction Fluid thickening improves safety of swallow in patients with oropharyngeal dysphagia due to shear, extensional and/or textural properties. We aimed to assess the effect of each of these properties of thickening products on post-stroke patients with oropharyngeal dysphagia. Methods We studied 4 commercial thickening products: A, modified starch; B and C, xanthan gum, and D, a mixture of the 2 and assessed a) shear viscosity at 25 oC and 50 and 300 s-1 before and after oral incubation, b) extensional deformation by the time to break up diameter, and c) maximal force, adhesiveness and cohesiveness with a texturometer. Results were correlated with videofluoroscopic studies assessing the effect of these thickening products on 267 patients with post-stroke oropharyngeal dysphagia. Results 1) Oral incubation reduced shear viscosity by over 90% for thickening product A and by 19%-35% for B, C, and D. All products presented shear thinning (50%-76%) in the pharynx. 2) Safety of swallow was strongly increased in a shear viscosity-dependent manner (P < 0.0001) and, moderately, by increasing maximal force (P < 0.0001). Residue was increased at different shear viscosity levels (P < 0.05). 3) break-up diameter varied greatly between thickening products irrespective of safety/efficacy of swallow; and d) adhesiveness and cohesiveness did not affect safety or efficacy of swallow. Conclusion Shear viscosity improved safety of swallow in a dose-dependent manner with all thickening products in post-stroke patients with oropharyngeal dysphagia and increased oropharyngeal residue. It was greatly affected by oral amylase in modified starch thickening products. Maximal force also moderately increased safety. In contrast, neither extensional deformation nor adhesiveness or cohesiveness presented any relationship with the therapeutic effect of thickening products in post-stroke patients with oropharyngeal dysphagia.