Even in summer, you should always be prepared for bad weather and pack a light insulated jacket!
You can choose between synthetic fibers and down. Down keeps you warm while taking a break but most often it is too warm for the activity itself. Synthetic fabrics have a worse weight-to-insulation ratio than down. However, they absorb sweat very efficiently.
Therefore, a light synthetic jacket such as Haglöfs Touring Insulation Jacket is a good solution for activities at lower temperatures that also keeps you warm during breaks. This jacket is made of two different layers of QuadFusion fill with different strengths. This hollow chamber insulation material consists of recycled polyester and was originally developed by Haglöfs. The outer surface of the Touring Insulation Jacket is water repellent, windproof, and resistant against abrasion. The jacket keeps you warm at all times, even when wet. You can wear it both as an outer or mid-layer and pack it into its hood. Thus, its packed dimensions are reduced to a minimum and you always have some weather protection handy in your backpack.
The Touring Insulation Jacket can hardly be categorized. In fact, it is a thin and universally applicable insulation jacket with the great advantage that you can (and should) take it with you on any kind of tour.