I received this Glow by Daye Conditioning Heat Cap ($38) in a PR mailer a few months ago, and I fell in love with it the first time I used it. Before the last few months, I haven't always used heat on my hair when deep conditioning because, between the inconvenience of having to sit under a hot dryer for an hour or the noisiness of using a handheld dryer with a bonnet attachment, it always seemed like more of a pain in the ass than I liked for it to be.
This (obviously cordless) bonnet is designed so that you can put it in the microwave for a few minutes and wear it as a deep conditioning cap for 30 minutes to an hour. The secret behind how it stays warm for so long after leaving the microwave is the fact that it's made with flaxseed that helps with retaining heat.