Choosing between two jackets usually comes down to price and features. The variable that determines environmental outcome is neither, and it is rarely printed on the label.
The footprint is front-loaded
Nearly all of a garment's impact occurs before purchase, in fibre production, fabric manufacture, assembly and freight.
Using it adds comparatively little, since washing is occasional and no energy is consumed by wearing it.
Dividing that fixed impact by the number of years of use gives an annual figure, and the only lever with real leverage is the denominator.
Durability is constructed, not claimed
Longevity comes from identifiable features: denser face fabrics, reinforcement at abrasion points, bar-tacked stress points, quality zips and generous seam allowances.
These add weight and cost, which is why the most durable garments are rarely the lightest, and why ultralight equipment is inherently shorter-lived.
Warranty terms are a useful proxy, since a manufacturer offering long coverage has priced in the expected failure rate and is signalling confidence.
Repair support extends life beyond the first failure
A garment reaching its first significant failure either enters repair or enters waste, and which happens depends largely on whether repair is available and affordable.
Brands running repair services, stocking spare components and publishing repair guidance keep items in use through several failures.
Independent repairers cover much of the same ground, and a zip replacement typically costs a fraction of a new garment while restoring the item to full function.
Availability of spare parts is the quiet determinant here, since a proprietary buckle or a discontinued zip size can render an otherwise sound garment unrepairable.
Over-specification is a hidden waste
A shell built for sustained mountain use represents considerable manufacturing impact, and buying one for commuting in occasional rain incurs that impact for capability never used.
Matching the specification to actual conditions is a genuine reduction, and it usually costs less as well.
The opposite failure is equally wasteful. Equipment that is inadequate for the conditions is replaced quickly and the impact is incurred twice.
Fashion cycles work against all of this
Seasonal colourways and annual model updates encourage replacement of functional items, which is the mechanism by which durability is undermined commercially.
Buying in neutral colours from ranges carried across several seasons reduces the pressure, and it makes spare parts more likely to remain available.
The most environmentally sound jacket is generally the one already owned, maintained properly and repaired when it fails.