Denim has more mythology per square centimetre than any other fabric. Part of it is earned — genuine selvedge denim from old shuttle looms is genuinely different from commodity denim. But a large part of the language around denim exists to create pricing power, not to transmit useful information.
Selvedge: real difference, overstated significance
Selvedge denim is woven on narrow shuttle looms that produce a self-finished edge, which eliminates fraying at the outseam. The finished-edge outseam with the selvedge showing is a distinctive construction detail with genuine visual appeal. That much is real.
What is overstated: the claim that selvedge denim is inherently more durable, more beautiful, or more authentic than non-selvedge denim. A high-quality projectile-loomed denim at 14 oz will outperform a poorly-made shuttle-loomed selvedge in every wear test. The loom type is a production method, not a quality guarantee.
Ringspun vs open-end: the gap is closing
Ringspun yarn is spun in a continuous twisting process that produces a tighter, smoother yarn. Open-end spun yarn is faster and cheaper to produce with a slightly harsher hand feel. The difference was more significant thirty years ago. Modern open-end spinning equipment produces yarn that is difficult to distinguish from ringspun in a finished garment. If a mill charges a significant premium for ringspun without being able to show you a comparative hand-feel sample, push back.
What actually matters
What actually matters when you spec denim: weight (oz per square yard, confirmed post-wash), fibre content, weave structure (3×1 twill, 2×1, broken twill), shrinkage after three washes, stretch recovery for stretch denim, and colour fastness. These numbers tell you what the fabric will do. The stories about Japanese mills and antique looms will not help you when your seams are puckering after the first wash.