The main advantage with choosing a synthetic option over down is its performance when wet. Downpours happen and down insulation absorbs moisture, allowing water to take up the space where warm air should be. This majorly impacts the garment’s insulative abilities. However, a synthetic option is made of plastic and as such will not absorb water to such a degree. Even when wet a synthetic, insulative jacket will maintain upwards of 90% of its dry, insulative performance.
Furthermore, a synthetic jacket is much easier to care for. It can be washed with standard non-bio washing detergent or a technical-wear-based product such as Nikwax Techwash on a regular 30-degree cycle and then tumble-dried on low heat. A down garment requires a few more steps and careful drying.