Yes. The official BF undergarment is spacifically a "Craft" brand base layer t-shirt. There is no acceptable substitute. Only bike stores will have them and, even at that, you may have to go into the back room and whisper to the mechanic to get them to sell you one. I'm only telling you this because I like you. I don't ordinarily respond to questions posted by Haynes wearers.

At a ride that my wife and I did a couple years ago we bought commerative "wind shirts" for about $15.00. We wear them over our jerseys and they've been great! They are small and light enough to stuff into a small bag or jersey pocket but surprisingly warm.