Thank you to everyone for your replies. I have been looking carefully at the sites you have suggested and the results are very useful. However, I am still intrigued by the apparent disappearence of the firm I was looking for. It was mentioned in a thread sometime before Christmas on this forum. The topic included making a box air cleaner/filter, posters showed air cleaners they had built and put up pictures etc. and at some point somebody mentioned a site where you could buy filters. It was called Jason Filtration, or something like that, and it was the only site I have seen that publishes prices. Everywhere else wants you to contact them for information. That's OK but it takes time and I just wanted to find this particular site again. You know when you start something and you just want to see it through - I am at that stage now! I have tried the Search facility and have drawn a blank and Google is no help either.
Anyone remember anything now?
Let me know when this gets boring!
SF