It is rainy season in Chiang Mai & the north right now, and it runs May to October. The rain tends to come hard and short rather than all day, and it stays warm through it — so the thing to bring is a shell you can fold into a day bag, not a coat.
Going in February
The best months up here: dry, clear and genuinely cool at night — down to single digits in the hills, which surprises people packing for Thailand.
What this means for your bag
Layers, not one thick coat
Three thin layers beat one heavy one: they cover a wider range and pack smaller. A base layer, a fleece and a shell.
See the Winter Warmth Kit packReal sun protection
High-factor sunscreen, a hat with a brim and sunglasses. Reef-safe sunscreen is worth buying before you go — it is expensive and hard to find at the beach.
See the Beach & Pool Kit packQuick-dry fabrics
Cotton takes two days to dry in this air and starts to smell before it does. Synthetics and merino wash in a sink and are wearable by morning.
See the Summer Sun Kit pack
Agricultural burning fills the valley with smoke, worst in March. Views vanish, air quality can be among the worst in the world, and flights are occasionally affected.
What this means for your bag
A proper mask
A fitted FFP2/N95 — a cloth or surgical mask does nothing against smoke particles. Worth it if you have asthma or are travelling with children.
See the Health & Wellness packA layer for indoor air conditioning
Malls, buses and restaurants are cooled far below the street, and the swing is what makes people ill. A light long sleeve doubles as sun cover and as dress code for temples and mosques.
See the Smart Casual Evening pack
Build a packing plan around the season you are actually travelling in.