Ron,

Some manufacturers of flashes add a stiffening material at the back, whilst others do not. I would not try washing them - in all my 56 years of kilt wearing I have never washed, nor even thought to wash, any flashes; it's just not been necessary.

Woolite? I have sen this mentioned many times in posts here, but as far as I know it is not sold here in the United Kingdom, so I know nothing about it. I personally never wash wool unless absolutely necessary - the exception being kilt hose which I always wash by hand, adding a little fabric conditioner to the final rinse.

As has been recommended, a steam iron works well for me.