The non-specific adsorption of proteins on surfaces is a well-known and mostly undesirable phenomena, which is reduced by a surface coating with the linear polyether poly(ethylene glycol) (PEG) as the current benchmark material. However, the molecular mechanism of protein-resistant surfaces is still not fully understood. Two main hypotheses are generally applied. The first one is steric repulsion of the highly flexible tethered polymer chains, leading to an entropic penalty by adsorption of proteins due to the reduction in polymer chain mobility. The second one argues with well-hydrated polymer chains generating a repulsive interfacial water layer. In this article, we compare the three different protein-resistant polyether structures PEG, linear polyglycerol (LPG(OH)) and linear poly(methyl glycerol) (LPG(OMe)) to get new insights into the molecular mechanism behind protein resistance. In a theoretical approach, we apply an entropy estimator that assesses the conformational states of the tethered polyethers from MD simulations. It reveals the entropy differences between these polyethers to be in the order PEG>LPG(OH) > LPG(OMe). Moreover, experiments on fibrinogen adsorption of these surfaces via surface plasmon resonance spectroscopy are performed and correlated with the theoretical studies. We find that protein resistant properties of surfaces are likely to arise from an interplay of different factors.