Your hair needs to heat thoroughly to relax the cuticle edge and allow the absorption of key ingredients. Hood dryers are best because they evenly distribute the heat all over the hair at once. Using a hood dryer, you should be able to warm your hair thoroughly in about 15 to 20 minutes (a little longer for thick or long hair that has been gathered up).
Some other methods are sleeping with the plastic cap on your hair overnight after you have warmed up the cap with a hand held blow dryer, sitting in a sauna at the gym, warm towels wrapped around your hair or using the bonnet hair dryer that attaches to a blow dryer. When using any of these other methods you’ll need to increase the heating time to be sure to warm the hair evenly and completely.