How to decide if the article is clothing: Safety Aids
Some safety aids are designed in the shape of garments, and serve a subsidiary clothing function; for example waistcoat-style lifejackets or safety overvests with reflective strips for cyclists. Such items may be accepted as articles of clothing and eligible for zero-rating, subject to the design and suitability tests. Other safety aids which, although they may superficially resemble genuine items of clothing, have no such clothing functions (e.g. child safety harnesses and reflective armbands and waist straps) are always standard-rated.