Although modern military boots are very good and keep the wearer’s feet drier and better protected from the elements than at any time before, they can never be 100% effective and there are times, such as traversing marchland or boggy ground where water will still get into a boot and soak the wearer’s feet. Having cold, wet feet for any length of time is something that should be avoided and the British Army have a selection of waterproof liners available that can be worn over the feet and under the boot to help keep the wearer’s feet warmer and drier. These are in the form of an MVP (moisture vapour permeable) sock, in a mid-green shade:

The boot liners are made from the same goretex fabric as other waterproof clothing and the seams have been taped and glued to ensure water cannot enter through these as well. Each boot liner is stamped with a letter indicating whether they are for the right or left foot:

A label inside gives more information and a date of 1994 for these boot liners:

Opinion on the boot liners varies, one soldier was impressed with them:

Years ago, I was issued a couple of sets of Goretex boot inners whilst trialling the Combat assault boot prototype. They were the dog’s conkers for keeping your feet dry and warm, and were very comfy

Others were less enamoured:

First person in my unit who tried to tab any distance in the green booties ended up in hospital with open wounds that were beyond anything tinc benz could fix… 

Another agrees:

The old green booty liner(s) were blister machines

The boot liners seem to have been trialed in around 1984 and were clearly used and manufactured for a number of years, although they seem better suited to static duties rather than operations on the march. They have been replaced with more conventional black Sealskinz socks today.