Dress for two seasons and for cool water, not for the tropics you’re picturing. The Galápagos sits on the equator, but the currents keep the water cold and the mornings brisk. Light, quick-dry layers do the work. You’ll add and shed them all day.
There are two seasons, and they change what you pack. The warm, wetter season runs roughly December–May. The cool, dry “garúa” season runs June–November, with the mist heaviest July–September. Neither is a “better” time, but they call for slightly different bags.
Cool/dry season (Jun–Nov) — cooler water, garúa mist
Cooler air, cooler water, and a fine mist (the garúa) that peaks July–September. Pack a light rain shell and a real warm layer, a fleece or light down. You won’t be cold all day, but early small boat rides and overcast mornings are chillier than people expect.
Hot/wet season (Jan–May) — warmer water, sun and rain
Warmer water and warmer air, but with short, heavy downpours. You still want quick-dry layers and a rain shell, because the rain comes and goes fast. The sun is stronger now, so sun cover matters even more (more on that below).
The layer everyone forgets — a warm layer for small boat rides
Here’s the thing most first-timers get wrong: they pack for the equator and freeze on the water. Early-morning small boat rides and wind off the sea are cool year-round because the currents are cold. A fleece or light windproof layer is the item people wish they’d brought. Pack it whatever the season.