Nowadays, with the world at our fingertips courtesy of Google, I should have thought that a question such as this was easily answered. It was asked by Fiona while we were out visiting her father's airidh the other day.
The internet answers seemed equivocal with a general conclusion that the bog cotton could not be spun because it was not commercially viable, the fibres being too short. That rather suggested that if the fibres were too short it could not be spun at all - let alone commercially. But then I came across a craft site that showed bog cotton as a raw material but didn't go into any detail.
In the end the answer came by good old word of mouth thanks to one of those strange co-incidences that happen all too frequently. When a friend called at Fiona's house a couple of days later he said that he'd been out on the moor all afternoon - picking bog cotton for his Mum to weave.
Co-incidences like this are ever so common and my Latin master, Albert Wilson, pointed out that if you learned a new word it would almost certanly crop up again in no time. Ever since then I have called it Albert's Law. And Albert's Law worked again on the journey home. The answer to one of our crossword clues was Nautilus what should we then see in a shop window later in the day but this large pottery nautilus.