Are cheap Amazon base layers like WEERTI and DEVOPS actually warm enough?

For moderate cold and low-output activity (commuting, casual outdoor wear, layering under ski pants), verified-purchase reviewers consistently say yes, and r/BuyItForLife threads note they perform surprisingly well for the price. For high-output activities like ski touring or backcountry hiking, the fleece-lined polyester traps moisture more than merino, which can leave you cold once you stop moving.