The best replacement for flannel is plaid.

The best alternatives to flannel are rated as following:
★★★★★  plaid
★★★★  fleece
★★★  cotton sheets
★★  felt board
★★  felt
★★  jersey sheets
★★  cloth board
★★  fleece sheets
★  plaid difference
★  microfleece
★  muslin cloth
★  tweed
★  face washer
★  twill
★  percale
★  poplin
★  fleece warmer
  microfiber sheets
  jersey knit
  face cloth
  micro flannel
  chamois
  fleece fabric
  flannelette
  felt boards
  brushed cotton
  gabardine
  worsted

Your alternative for flannel is not listed? Suggest!
Speaking about flannel, one probably shouldn't forget about cardigan.

Other search terms related to flannel and their ratings are:
★★★★★ cardigan
★★ skater skirt
★ undershirt
You have in mind a companion for flannel and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of flannel in all years. Click on graph for more.
flannel
plaid
fleece