In reply to Simon Pelly:
> Thanks for the link and tips.
> So tried the shampoo trick but using fairy liquid. Brilliant.....
Brilliant as long as you do rinse thoroughly, could sting a bit otherwise. A bottle of supermarket own brand baby shampoo will cost you about £2 and last over a year even if swimming regularly. I just put the smallest drop on each lens, smear it around with my finger and rinse.
Apparently because any form of detergent destroys the surface tension the condensation on the inside lens can't form into the tiny droplets that make the lens foggy. And it seems to only need a very fine residue of detergent to work, not sure how long this fine residue will last before you need to re-coat.
I have a small hotel shampoo bottle that I have filled with baby shampoo and I keep in with my swimming kit so I apply before every swim.