Warm days and cool evenings might be the perfect combination (because who likes to sleep in the heat?); but you really need extra layers to make sure you're comfortable enjoying the great outdoors. Whether you are headed out on the water, watching the sun set from a lookout spot, or having one last dinner al fresco, a simple lightweight sweater made from natural material is the key to comfort. 

Stripes! This organic cotton sweater by Athleta has a slim cut with a stretch fit; perfect to throw in your bag as you head out for the evening. 

The A Detacher Klavdiya Pullover Sweater is made from a supersoft cotton and has a unique cross-body design that can be sexy (worn with short-shorts) or staid, but either way, a comfortable, relaxed way to cover up when need be. 

The subtly sweet pointelle-detail das pullover from Stewart + Brown is made from organic pima cotton and made fairly in Peru.

Gudrun Sjoden's eco-cotton cardigan comes in three colors and has a subtle print; fabulous paired with another print (try stripes or polka dots) or pretty matched with solids too. 

Suzanne Rae makes all of her clothes in New York City's garment district; this box sweater is meant to be oversized and super comfy, which is ideal for an extra layer, so whatever you wear underneath with work with it. 

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.