Finally, we compare the performance of the methods against experimental measurementis of microgel size for varying microgel concentration, for weakly-crosslinked ionic microgels in the salt-free limit. The system consists of loosely cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-PAA) microgels dispersed in deionized water at room temperature, neutral pH and various microgel concentrations c mic . We assume a salt-free solution since the samples were flame-sealed together with an ion exchange resin, which hinders the presence of additional salt ions. We assume that every microgel possesses a valence Z max = 3.7 × 10 4 , which has been measured combining conductivity titration and light scattering. We have considered N mon = 3×10 6 following Refs. , σ = 0.7 for NIPAM monomers and φ coll = φ rcp ≈ 0.64, resulting in a 0 = 83.68 nm. Taking x = N ch /N mon and χ as fitting parameters, we fit experimental measurements with the presented theoretical models. The experimental results are depicted in Fig. using points. Here, we plot the swelling ratio given by the microgel radius a over a reference microgel radius a ref , which is measured at the smallest experimental concentration c mic = 0.0167µM. We observe that the swelling steeply decreases with increasing c mic , tending to flatten at large concentrations. This behavior is similar to that in Fig. (presented in semilog scale). Fitted theoretical predictions for χ = 0.5 and x = 0.001 are plotted with continuous lines. Predictions from the different elastic models are indistinguishable in the presented scale. We see that both models accurately capture the microgel shrinking at low concentrations, while they qualitatively capture swelling flattening at large concentrations slightly underestimating microgel size. Fitting parameters agree with those obtained in Ref. , where a variation of the Gaussian model presented in Eq. ( ) has been used for describing then elastic pressure contribution. In Ref. , the effect of crosslinking is accounted for, while we have drop this contribution in order to agree with Langevin model in the limit of small deformation. Incorporation of this contribution leads typically to slightly smaller microgel size predictions, with marginal influence in the swelling ratio behavior.