Depending on Turbo location, heat shields rather than blankets or wrap can be a better solution.
Turbo blankets & wrap do a great job at reducing radiant heat but can cause significant problems as well.
Corky Bell posts occasionally over on the Miata forums & gives a bit of insight, i'll post a link to a similiar discussion over there.
regarding turbo blankets - MX-5 Miata Forum
Cheers, Trevor.