I am looking for a synthetic gilet for walking, not riding.
Any recommendations?
Buy one that fits is my recommendation. Both of my gilets are 1 size smaller than what I would consider buying if I was buying a gilet with sleeves.
If it's for use on the move, I'd maybe have a look at something like the Rab Xenair, which is designed to be relatively breathable. The problem with most insulated gilets and jackets is that fully windproof outer and liner fabrics tend not to be very breathable. Or something made using Polartec Alpha, which is designed to be active insulation, but not as outright warm.
If it's for warmth when stopped, I think synthetic fills are much of a muchness to be honest - Rab, Mountain Equipment etc, buy on fit would be my take. But I'd probably buy a jacket rather than a gilet for that anyway.
I have a decathlon special. Weight to warmth ratio is phenomenal. It's just council spec insulation in a windproof outer.
Very versatile, over a fleece or inside a primaloft jacket. Even in sleeping bag.
Close fit is key so consider downsizing as above