Billed as the lightest gilet on the market - which it isn't - Rapha's Emergency Gilet is still light and compact, especially in its sausage-shaped stuffsack, which fits under your saddle.
It's made from Pertex Quantum, a thin wind- and shower-proof synthetic that feels very like the fabric of the Optik. The sides and most of the back are mesh for breathability; the hem is elasticated, and the slightly dropped tail has a Pertex panel for spray protection.
The collar is adjustable, thanks to Velcro, so it can be made quite snug. There's reflective piping across the upper back and a little breast pocket that would easily fit a phone. The cut is quite close, although I wore Small rather than Medium at Rapha's suggestion. When packing the gilet, be careful to avoid snagging the mesh with the Velcro.
Rapha pitch this as a get-you-home garment rather than all-day wear. It'll do that just fine, but so will the Adidas, Optik or Conti gilets, which are £40-£60 cheaper.