Pack for a swing of 10 to 15 degrees between a sunny afternoon and the hour after dark, not for an average temperature. Three light layers beat one warm coat everywhere in Bhutan. Cover your shoulders and knees for monasteries and dzongs, which is expected rather than optional, and bring shoes you have already walked in and sun protection you will use.

Layers, because of the swing

Bhutan's weather follows altitude and sun more than season, and an ordinary week crosses a lot of altitude. On a western route you sleep at 2,400 metres in Thimphu, drop to 1,300 in Punakha where the rice grows, cross a pass at 3,080 and walk up to 3,120 at Taktsang.

A single warm coat solves the evening and is dead weight from ten in the morning. Three light layers cover every hour, and the one you aren't wearing goes in the daypack: two or three merino or synthetic t-shirts (they don't need washing daily, and cotton does), a light fleece or a thin down jacket that packs to nothing, and a shell that keeps out wind and showers. The wind on a pass is what turns a pleasant day cold, and it can rain in any month.

Pack for the swing, not the average. The average is a temperature you'll never feel.

What the dzongs expect

Shoulders and knees covered in monasteries, dzongs and temples: long trousers, and sleeves rather than a vest. Hats come off inside, and shoes come off wherever your guide's do.

The reason tells you where the edges are. Dzongs are working buildings: the district government sits in them and monks live in them. Bhutanese visitors come in gho and kira, with a formal scarf for the inner courtyards. Nobody expects you to match that, only to look dressed for a place where people are working and praying. Nobody will measure a hemline; someone will notice a vest.

So one pair of long trousers you find comfortable is worth more than three you put up with. You will wear them almost every day.

Thimphu, at 2,400 metres: bright afternoons and cold evenings, the pattern for most of a week in the west.

What changes with the season

Two things hold all year: sun protection and something windproof. At 3,000 metres the sun burns in a way the air temperature doesn't warn you about.

What people get wrong

The commonest mistake is the big coat. People read "Himalaya" and pack for an expedition, then carry it all week for the two hours after dinner. Unless you are travelling in December or January, or sleeping high, a down jacket that squashes to the size of a water bottle is the right amount of warm. The second is a spare pair of boots: one comfortable pair covers Taktsang, the valley walks and the dzongs.

The things people forget are lip balm, which everyone asks for by day two in the dry air; a head torch, for power cuts, dark temple interiors and early starts; and any regular medication, which should travel in its labelled packaging with a copy of the prescription. That is a formality at the border, and far easier to sort before you leave.

If we could insist on two things, they would be shoes and a bottle. The Taktsang day is about 10 km with 870 metres of climbing and some 1,400 steps in the gorge, and new boots turn it into a day about blisters. If your only walking shoes are old and comfortable, bring those. And bring a bottle you will refill. Bhutan's constitution commits it to keeping most of the country under forest, and a week of bought plastic sits badly with that. Boiled and filtered water is available everywhere, and we would rather refill you than sell you bottles.

What we won't do is promise you a temperature. We'll tell you where you sleep each night and how high it is, which is a more useful forecast and one we can stand behind.

Your bags, and a trek

On cultural routes your luggage travels by vehicle, so a soft bag is easier than a hard case, and you never carry more than a daypack during the day. What we supply in the way of equipment depends on the route, so ask us and we'll answer for yours.

A supported trek is a different list rather than a longer one: sleeping above 3,500 metres, a sleeping bag rated for the camps, a duffel a pack animal can carry, and boots that cope with eight wet days rather than one.

The route matters more than the month. The Sacred Valleys stays between 1,300 and 3,120 metres and never sleeps high, so the list above is all of it. The Heart of Druk adds Phobjikha, noticeably colder at night than anywhere else on a cultural route, and the one place a winter-weight layer isn't over-packing. The Chomolhari routes sleep high for several nights running and need the trek list, which we send before departure.