There is always a danger of fire within an armoured fighting vehicle, with fuel and explosives being carried in a confined space. A lot of effort is spent on trying to reduce the risk of fire, and on fighting that fire quickly before it can take hold but there always remains the risk of a flash in combat that happens too fast for the fail safes to kick in. In order to protect the crew from such flash fires, fire proof clothing is issued, much like that used by the Royal Navy on board its ships. The head is particularly vulnerable and so a special fire proof balaclava is issued:
This is designed to be worn underneath a helmet and coveralls, and has a long skirt at the neck to protect this area, with flaps that can be tucked into the collar of the coverall to protect all the skin:
When placed on the mannequin it can be seen how far onto the chest this balaclava stretched and with a set of overalls zipped up to the neck there is no exposed skin left vulnerable:
Holes are provided for the wearer’s face and for each of his ears to allow him to continue to hear whilst wearing it. As AFVs use internal communications with headsets, the wearer’s ears would be protected by his headphones anyway:

A label inside indicates that the balaclava is fire resistant:
To ensure it is fireproof, the balaclava is made of Aromatic Polyamide, Science Direct describes these fibres as:
5.18.3.4 Fully Aromatic Polyamides or Polyaramids
Fully aromatic PAs, in case of polyaramids, are defined as homo- or copolyamides consisting of at least 80 mol.% aromatic monomer units. They are typically intrinsically flame retardant, have very high melting points, and show nematic liquid crystalline behavior. Therefore, these materials are processed from solutions, in which the para-linked aramids exhibit lyotropic behavior, making them suitable for high-strength fiber production. Typical examples are polyaramids based on p-phenylenediamine and terephthalic acid (Kevlar®, Twaron®) and based on m-phenylenediamine and isophthalic acid (Nomex®). The all-para polyaramid fibers are, for example, used for bulletproof vests and other armor plating applications, whereas the all-meta polyaramid-based fibers have a higher wearing comfort and are used for overalls, for example, for fire fighters.
I hope that makes sense to some of you, because a lot of it is beyond me!