Methods and apparatus of the present invention provide viscoelastic barrier materials for use as barriers in devices such as pressure measurement catheters. Improved barrier materials sometimes include at least one barrier material precursor combined with an amount of a softener. In other embodiments, two barrier material precursor components are combined without a softener to provide a fully cross-linked barrier material having certain softness characteristics. In various embodiments, a softener may be dimethyl silicone oil and may be combined with a barrier material precursor in an amount of between about 25% and about 45% by weight, relative to the final barrier material. Once a viscoelastic barrier material is prepared, it may be placed in a pressure transmission catheter or similar device, for example by injecting the gel into a lumen of the catheter via a syringe. Barrier materials of the present invention have one or more advantageous properties, such as a desired softness, full cross-linking, resistance to washout from a catheter, enhanced stability and/or the like.