Between floor joists

[chilly7]

Hi, I'm new here and would ask :-

Have a joisted floor with about 400mm space to solum. The builders about 14 years ago only put in mesh with fibre glass lying on it. This is now sagging and, (I think) not doing much.
I am thinking of removing this and putting a product like Celotex or Stratherm, with nailed strips accross the joints to support it.
Anyone advise me on correct thickness, say 100mm, and what would be the best ? Thanks in advance.

[chilly7]

Sorry ecos, did not realise your my topic was so similar as yours !!!
chilly7