I've never bothered up until I bought my new S-works helmet which is far more vented so bought a cheapie skull cap type thing from Lidl or Aldi (always get mixed up) which was about a fiver - worn it on every ride I've had out since - not too tight so dont over heat in it but its quite deep around the back and sides so covers my ears (which I'm more than blessed in) and keeps the upper neck warm too - combine this with a buff round the neck when its really cold.