Mazda MX-5 Miata Forum : “Are convertible tops (not the hard top) able to keep driver warm in winter mont...”

Yes, the tops are designed to seal and hold heat/air. Unless you have a problem with how it seals, you'll be fine.

oh yes, infact if its on recirculate i find myself opening the window with it being close to 0 degrees F that heater really kicks in the small cabin!

Yes, the Miata heater does a great job, even in very cold temps.

yeah they're great, though i normally drive mine with the top down, as long as its not raining or snowing, lol

Absolutely the soft tops work fine! I live in Northern Alberta and the winter temperature here has been minus 20 to 30 C, and I've been turning the heater down because it's cooking me!