I assume you're talking about blown-in sheep's wool fiber insulation. I have never used it. I have used both wet-spray cellulose as well as netted and blown-in cellulose, and both high and low-density spray foam insulations in walls; blown-in cellulose in attics and spray-foam insulation in cathedralized, conditioned attics.

The R-value of high-density spray foams will be higher than cellulose and it will be easier to insulate behind electrical rough-in boxes. I've found they perform comparably with regard to air infiltration. At present in our market, cellulose insulation costs a whole lot less than spray foam. If you go for the sheep's wool insulation, just check the fine print to make sure they don't force you to take delivery of a pallet load of mint jelly. It's awful stuff.

Hi Ross Thank you. I should have been more specific it’s blown in blown in wool fibre with the netting. We are learning towards the spray foam open cell. We live in Ontario cold winters. I appreciate your response.

Thank you mojavemaria

In Ontario you'll need R-30 to R-35 for the wall assembly. You won't get much R-value with low-density spray foam insulation.

We had a home in the mountains and did spray foam all exterior walls and ceiling- we had radiant in floor heat and no AC (so there were no ducts either) - because of this we had to install an ERV to get fresh air inside - something to consider if you’re in the same situation. It added close to $5k to our build - and that was in 2017.