Alternatives to 40mm Steico Protect dry internal wood fibre board

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My build up for the walls and roof includes a layer of 40mm Steico Protect dry internal wood fibre board. This is out of stock with all the merchants I have approached (Mark Wye, insulationsuperstore and ecomerchant) and most are quoting very long lead times of up to 10 weeks. Can anybody suggest an alternative which would have the same decrement delay properties.

Someone has suggested Phenolic Foam based product Kooltherm K7, made by Kingspan, on the basis that it has a density of 200kg/m3, but I don't think it will have the same decrement delay just because of the density. Any thoughts?