Just wanted to add i've been looking into this lately as i was wondering about washing my flips. With regards to BG products the website says the warranty is invalid if:
Any of the following has been used in conjunction with the use/care of the product:
* Water temperatures exceeding 150F or 60C
* A detergent containing additives (enzymes, brighteners, whiteners, dyes, perfumes, essential oils) or natural soap
* Fabric softeners
* Any caustic substance
* Diaper rash cream
So that defo rules out bio as it contains enzymes, I assumed non-bio would be ok, but looking at the ingredients on most of the 'big brands' their non-bio products still contain optical brightners. The only one i've found so far which doesn't contain optical brighters is Ecover.