Viscoelastic characteristics of magnetic tapes with poly(ethylene naphthalate) substrates were studied using experimental techniques. Measurements were made using samples cut from commercially available tapes, and solvents were used to remove front and/or back coat layers to obtain substrates and dual-layer samples. Experimental results allowed for fundamental compliance and viscosity parameters to be determined using a Kelvin-Voigt model. Rates of creep-compliance were also predicted, and comparisons were made with results for tapes that used poly(ethylene terephthalate) and aromatic poly(amide) substrates. Dynamic mechanical analysis (DMA) was used to help make correlations between viscous characteristics measured from the creep-compliance results and molecular characteristics of the substrates. Time-temperature superposition (TTS) was used to predict creep-compliance over extended time periods, and a rule-of-mixtures method was used to predict the compliance of constitutive layers. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 899-916, 2009