Acornwrote a review of Assos Skinfoil Winter Long-Sleeve Base Layer - Men's on November 9, 2019
Familiarity: I've used it several times
The Assos Skinfoil is an unusual baselayer design. It is made of 95% polypropylene and 5% elastane (Spandex). The Skinfoil is designed to wrap your body like a skin suit. When I first removed the size 0 Skinfoil out of its packaging, it looked like an outfit for a 10 year old. The garment is very elastic, it compresses the body, but I don't feel suffocating, and it does not restrict any movement. When I wear the Skinfoil underneath a fitting jersey or jacket, there is no extra fabric bulge and folds to deal with. This is very different from wearing a fleece baselayer; fleece is bulkier, heavier and more restrictive. Polypropylene fabric is one of the lightest synthetic fibers in existence, the thermal conductivity of this substance is lower than that of most synthetic fibers, which means that it is ideally suited for cold weather wear. The fabric does not absorb water, so all your sweat is wick towards the outer garments. While this fabric's moisture-transferring properties are highly desirable for sportswear, the inability to wash this fabric with hot water makes it hard to remove odors from polypropylene sportswear. The new Skinfoil has a fragrance to it, it's probably the anti-odor treatment I'm smelling. Given the fabric's limitation, I make a habit of washing the garment immediately after each use and use cold water only. By the way, polypropylene fabric in general is susceptible to UV damage, so don't use it as an outer layer, or wear a long sleeve Skinfoil under a short sleeve jersey all the time.
I was riding outside this morning in 40 degrees cloudy weather. I paired the Skinfoil with an Assos Mille jacket. At the beginning of the ride, I was warm, but not toasty warm, and I could feel the chill in the air. But it was not frigid and the body did not tighten up. After a few minutes when the body got warmed up, it felt very good. The chilly wind was in my face, but the body stayed loose and comfortable. Towards the end of the 90 minute ride, my body was warm, but I did not feel drenching in sweat or overheated. The Skinfoil was slightly moist from the sweat and it formed a layer of cooling fabric. I did not feel wet at all, just a cool fabric against my warm body. It felt pretty good, comfortable, no overheated or frigid body. Once I went indoor, the Skinfoil dried up in just a few minutes, I didn't feel the need to take it off right away.
As for the sizing, I'm 5'7", 135 lb., and my chest size is 38". The Assos web site as well as their Switzerland support folks recommended a size 0. All my Assos jerseys and jackets are in SMALL. The Skinfoil in Size 0 fits me like a glove. I don't know why the Competitive Cyclist site shows a size 0 for XXS/XS and a size I for S/M, that is different from the ASSOS recommendation.