The 1970s early 1970s
Cheesecloth and Gauze
A cheap, loosely woven cotton meant for straining curds became, almost by accident, the signature fabric of early-70s boho dressing.
Cheesecloth is a genuinely odd fabric to find at the center of a fashion decade - it's a loosely woven, lightweight cotton gauze, originally and still literally used for wrapping and straining cheese curds, with almost no structural integrity on its own. That looseness is exactly what made it so appealing to a generation of dressers actively rejecting the previous decades' structured tailoring, and it arrived cheap enough that a garment made from it cost almost nothing next to a proper woven blouse.
Its texture and near-transparency made it a natural match for the loose, unlined, often smocked construction of the peasant blouse, where the fabric's crinkled, slightly uneven hand read as handmade and organic rather than cheap - a real reversal of how a fabric with essentially no manufacturing polish usually gets received. It also took hand-dye and tie-dye extremely well, being a loosely woven, absorbent natural fiber, which is part of why so much surviving cheesecloth clothing from this specific window carries visible hand-dyed color variation rather than the flat, even printed color you'd see on a factory textile - genuine amateur craft, not an aesthetic imitation of it.
Gauze, the slightly more tightly woven cousin fabric often used interchangeably in period sewing patterns, filled the same role in slightly sturdier garments - tops, dresses, even light trousers - built for the loose, flowing lines of the bohemian-prairie silhouette that dominated 1970 through about 1974. I think what's genuinely notable about cheesecloth's moment is how directly the fabric's own limitations became the point: it wrinkles instantly, it can't hold a tailored line, it's borderline see-through worn on its own - all qualities that would have disqualified it from serious fashion a decade earlier, and all qualities that made it exactly right for a moment that had decided structure itself was the thing to reject.