First is to understand that sustainability is not a single element. It is multifaceted and addresses many concepts. This diagram below gives you a good understanding of how complex the definition of sustainability can really be.
Sustainability covers not only items like materials to determine if they are sustainable, it also covers economy and social practices as well. If a company is supporting a village and providing them livable wages and ethical working conditions or creating a new efficient technology that increases jobs, this can be considered "sustainable." Source: http://www.gettingtosustainability.com.au/about-sustainability/
But I'm not going to spend a lot of time on the social and economic aspect though I recommend looking further into them. Today I want to touch on materials that you want to look for when shopping for fashion and home goods.
Cotton: This can be tricky because typical cotton usually is drenched in chemicals and can be a GMO product. You need to look for organic cotton, it is safer for you and the environment.
Bamboo and Hemp: Hemp has been around for thousands of years. It is naturally pest resistant, grows like a weed, he he, and is durable. Hemp is also used in a lot of medicinal items and for nutrition, this plant is a huge asset to our world and being very under utilized. Bamboo has slowly become a new favorite material, one stock of bamboo can be used for fabric, flooring, paper products, and even food. Once it is cut it will regrow from that stock and it grows very fast. It uses minimal land and maximizes usage.
Wool: If you are vegan then wool and silk will not be an option for you. If you are not vegan then you can find wool that has been ethically sourced. Ethically sourced simply means the animals are treated humanely. They are living on some land, fed good food and are sheered in a minimal stress environment. If the company isn't giving you that information, just ask! If you are unsure of what materials are being used to make something or if the animals are being treated well, it is always a good idea to contact the company.
Silk: Again, silk is made from silkworms. A humane or ethical silk is that they harvest the silk when the worm has gone through metamorphosis and has left the silk ball behind. Silk is sustainable because you are simply taking a waste product from an animal and silkworms need minimal space. If you are looking for this type of silk it is commonly called "peace silk." And ask if the company doesn't highlight it.
Other Sustainable materials: There are some new wacky stuff coming onto the market, things like fibers made from sour milk. Huh? And even from coffee grounds but one that keeps popping up a lot is Tencel. Tencel is made from wood pulp and I have personally heard from fabric users that it is a good product. It is soft and makes good wearable garments, seems like it comes up a lot in everyday wear and active wear. It is always good to see what people are starting to create in order to add more sustainably options to the fabric world.
This is just the tip of the ice burg of sustainable materials. If you want to read more about the leather options check out my post here:
Ok the biggest fabrics to avoid is polyester, nylon, and acrylic based fabrics. The polyester cotton blend is the most popular material you will find to date. Any plastic based material, unless it is from a recycled source, will be a bad option and unfortunately it's EVERYWHERE! You will find more toxic unsustainable fabrics on the market then sustainable because it is cheap, cheap, cheap. But the good news is, the more consumers look for sustainable fabrics, the more the market will swing towards more sustainable materials.
And if you see something on a website that seems weird always do a little research or contact the company and request more information.