Underfloor insulation thickness

I'm looking at installing insulation under my suspended floor. The joists are 120mm deep. My plan is to use loft insulation held in place by netting.

Loft insulation isn't readily available in 120mm thickness though, so I'm looking at 100mm or 150mm. Which is best? 100mm will leave a gap immediately under the flooring, but if I pack in 150mm it'll be quite dense so I'm wondering if it might trap moisture?

colinmac, good evening.

Are you intending to lift the existing flooring?

As an aside, the insulation should leave no gaps between it and the underside of the flooring.

Ken.

No, I'll be installing from below. The "leave no gaps" advice is what I'm looking for, so I'll go with 150mm insulation. Thanks.