Type I, or IEC I, ferric or normal cassettes were historically the first, the most common and the least expensive; they dominated the prerecorded cassette market. The magnetic layer of a ferric tape consists of around 30% synthetic binder and 70% magnetic powder — acicular (oblong, needle-like) particles of gamma ferric oxide (γ-FeO), with a length of  to . Each particle of such size contains a single magnetic domain. The powder was and still is manufactured in bulk by chemical companies specializing in mineral pigments for the paint industry. Ferric magnetic layers are brown in colour, whose shade and intensity depends mostly on the size of the particles.
Type I tapes must be recorded with normal (low) bias flux and replayed with a  time constant. Over time, ferric oxide technology developed continuously, with new, superior generations emerging around every five years. Cassettes of various periods and price points can be sorted into three distinct groups: basic coarse-grained tapes; advanced fine-grained, or microferric, tapes; and highest-grade ferricobalt tapes, having ferric oxide particles encapsulated in a thin layer of cobalt-iron compound. Ferricobalt tapes are often called cobalt doped, however, this is historically incorrect. Cobalt doping in a strict sense involves uniform substitution of iron atoms with cobalt. This technology has been tried for audio and failed, losing to chromium dioxide. Later, the industry has chosen the far more reliable and repeatable process of cobalt adsorption — encapsulation of unmodified iron oxide particles in a thin layer of cobalt ferrite.
The remanence and squareness properties of the three groups substantially differ, while coercivity remains almost unchanged at around  ( for the IEC reference tape approved in 1979). Quality Type I cassettes have higher midrange MOL than most Type II tapes, slow and gentle MOL roll-off at low frequencies, but less high-frequency headroom than Type II. In practice, that means that ferric tapes have lower fidelity compared to chrome tapes and metal tapes at high frequencies, but are often better at reproducing the low frequencies found in bass-heavy music.