Back in the day, undercrackers, especially those worn in winter, were made of fine wool.
Commercial woollen underwear, 1920s.
Wool was a huge, huge industry in most Western countries. We cannot imagine, today, with cheap off-the-peg clothing imports, what the wool industry was like before the 1970s. Think Amazon, think eBay, think Microsoft: that sort of big. Just getting dressed was a major part of life, before you could pop into Primark and come out with a complete wardrobe, including smalls, for £10–20. In my grandparents’ day, it meant going to a tailor for your decent outdoor and winter clothing, purchasing rolls of cotton or linen to sew your summer clothing, and knitting, knitting, knitting in every spare moment to provide yourself and your family with socks, underwear, gloves and other ‘comforts’. For many families, it meant carding and spinning the wool, before knitting. Much of Great Britain’s former wealth, and its Industrial Revolution, was driven by wool.
And so, of course, when sea-bathing became the In thing to do in the Victorian era, the outfits were naturally made of wool – though usually woven flannel fabric, rather than knitted.
This fabric did not sag and expand (much) when wet, and if it did, so what? It just meant it covered up more of the body, which was the point of these cumbersome outfits.
It was only when fashions changed to more skimpy swimsuits that it became apparent that wool, particularly when knitted, wasn’t ideal: the sagging then revealed more than hid.
But there’s no reason to avoid crafting your own swimwear: crocheted cotton is a sturdy fall-back –
and even wool is okay, if you work with its qualities rather than against: