One way to get faster, it seems, is to leave the city cycling paths (which are often shaded by trees) and to head to long stretches on country roads.
On 4+ hour rides my arms get scorched from the sun, and it's cumulative. This is the case despite applying a famous-brand high-SPF sport-specific cream at the start. Reapplying every hour or two is not a great solution. It seems better to cover up.
Many "arm warmers" in the form of sleeves are available on the market, and these could potentially be used even in 30-35°C weather, subject to drinking a bit more along the ride, but the overheating would be unpleasant.
The very seasoned (from their looks they seem to spend entire days riding) cyclists that I encounter have almost always covered forearms, sometimes with what looks like a material that sits just a few millimeters from the skin—one with ventilation holes. Rather than make a U-turn and ask them, I thought I'd ask here.
What is a good fabric to protect forearms in 30+°C weather?
Companion question: Vuelta a España, Tour de France, and Giro d'Italia take place in the height of summer, and the very many competitors ride far longer and in arbitrary weather. Yet they don't seem to bake their skin from the sun, and they certainly neither stop to reapply creams nor wear arm covers. What solution do they use?