The current standard for organ-on-chip substrate materials is polydimethylsiloxane (PDMS). PDMS has many beneficial properties such as biocompatibility, transparency, elasticity, and easy prototyping. The main disadvantages of PDMS are its hydrophobicity (reducing cell attachment and cell proliferation), quick hydrophobic recovery (within a few hours) after surface modification, and unselective absorption of small molecules, altering drug concentration during testing or causing cross-contamination between channels. To overcome these shortcomings, an alternative material lacking the disadvantages and retaining the advantages of PDMS is needed in the field. Ostemer 324, Ostemer 220 and a variation of PDMS (PDMS+) were characterized to determine whether they would be a suitable alternative to PDMS as substrate material. The materials were compared to PDMS and characterized for spin-coating and curing on silicon wafers, moulding, etching, surface wettability before and after surface modification (plasma treatment), stiffness, optical transparency, biocompatibility and absorption of small molecules. The results of this work show that Ostemer 324 appears to be a promising alternative, with similar characteristics to PDMS. The main advantage is its hydrophilic surface, which becomes even more hydrophilic after plasma treatment, and slow hydrophobic recovery rate. However, its curing time is longer, the material is stiffer and not easy to mould. Ostemer 220 shows very poor adhesion on Teflon coated silicon wafers, is hard to mould, and shows inconsistent results during biocompatibility testing. PDMS+ is very similar to PDMS, and improves upon the latter in terms of surface wettability after surface modification, hydrophobic recovery and small molecule absorption.