In the real world we know this stuff as Lycra or Spandex. Lycra originated from research done during the Second World War into substitutes for rubber. Its most obvious properties are:

• It stretches easily and a lot – up to 500% its length at rest;
• It’s tough. Flexi-floss can resist cutting with scissors and shrugs off fishing abuse;
• It takes colour easily and takes dye easily (we usually see Flexi-floss already dyed). It can be coloured with permanent marker pens.

I’m not sure who decided Lycra strands make good tying material but he/she was right. Far tougher than rubber or latex, which was and is used in tying, Lycra doesn’t tear easily and is much less vulnerable to the UV in sunlight.

These are large spools, no quantity on the spool, but a generous helping. The range of colours here is interesting, but in reality I would plump for four of them; red, black, chartreuse and white. Why those? Because I use more red than any other Flexi-floss colour, black comes second and is a pest to dye, chartreuse because it’s vivid (appeals to my inner tying ‘magpie’), white because I can dye it any colour or shade it with pens (and I need orange which is not included in this selection). That, and pink, purple, tan, blue, and brown don’t figure in much of my tying with Flexi-floss and this particular yellow is a little on the insipid side.

Flexi-floss/Lycra is made up of extremely fine filaments which bond together during manufacture into a coherent bundle, we treat it as one strand. These Flexi-floss strands are fine and roughly rectangular, as are most. For tying that only really means we need to be aware that winding a strand around a hook-shank causes the strand to twist and since these are rectangular strands twisting will show as a bump on the body of a fly.