You know the deal, heat it up and it shrinks. Use it to cover solder joints to prevent shorting which can ruin your day. Available in 3.2mm and 4.6mm unshrunken diameter. 3.2mm will suit most applications fitting both 18 and 16 AWG wire nicely however it won't fit over XT60 terminals. 4.6mm is better suited for that.
Price is for one 20cm length.