Continuing to dispel the notion that its fast fashion model is out of kilter with the apparel industry's increasing focus on sustainability issues, retailer H&M is ramping up its eco-credentials.

The company's latest Conscious and Conscious Exclusive collections add new materials to a line-up that already includes organic cotton and hemp and recycled polyester.

For the first time, H&M will be using organic leather from Swedish leather supplier Tärnsjö, which comes from cows bred for organic meat production, and organic silk cultivated in organic mulberry trees.

The materials will appear in the limited-edition Conscious Exclusive collection, which will be available in 150 selected H&M stores worldwide as well as online. The collection is made in collaboration with the sustainable fashion and design think-tank Ever Manifesto.

The moves build on H&M's existing pledges to buy 100% of its cotton from more sustainable sources and phase out toxic chemicals from its supply chain by 2020. It is also working to close the loop in its clothing, and recently launched a denim collection made from 20% recycled cotton from its Garment Collecting Initiative.

While it's something of a paradox about the fashion industry that it keeps consumer interest by feeding through fresh merchandise - which is in complete contradiction to sustainability - H&M's efforts have also seen it recognised for the fourth time as one of the world's most ethical companies.

The accolade from US business ethics think-tank the Ethisphere Institute makes H&M one of only three companies in the apparel industry honoured for 2014, the other two being Gap Inc and Levi Strauss.

Hong Kong based sourcing specialist William E Connor & Associates and UK retailer Marks & Spencer were also recognised in separate categories.

Scores are generated in five key categories: ethics and compliance programme (25%), reputation, leadership and innovation (20%), governance (10%), corporate citizenship and responsibility (25%) and culture of ethics (20%).