Canvas?

Any bag will create an environment perfect for growing mushrooms is you don't look after it. Mould hates bright light and fresh air, so whatever you use, make sure you don't leave damp kit in it in a dark cupboard. Take everything out after a rainy day and allow it all to dry thoroughly.

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UK wedding photographer in the Lake District
http://www.johnleech-weddingphotography.co.uk
For my landscapes and fine art photography:
http://www.johnleechstudio.co.uk