Bolt threads does not worry me that much, apparently they have reached huge obstacles in their approach which they can not easily avoid. They use yeast to produce spider silk, which is easily scaled up, beer brewing has been established centuries ago.
Yet they claim that they sold the first batch of their Microsilk ties two and a half years ago, sold a batch of caps two years ago and created a dress from Microsilk two years ago. And never produced a single one of them ever again. Yeast fermentation takes days, there is no other answer to the question "Why are they not producing anything?" than their technology is not suitable to produce silk proteins in the purity and quantity needed for a price anyone would pay for it. The Moon parka has the same drawback, it was first announced in 2015, yet not a single unit was sold they simply announced it again this year.
As a molecular biologist, their two main weak points must be the protein isolation and the thread spinning. If you produce a protein in bacteria, fungi, mammalian cells, whatever, you will get a thin broth of the protein that contains literally thousands of other proteins, polysaccharides, cell debris, which all are totally unsuitable to produce threads from.
On their website they only state they "isolate and purify" the protein. This can be immensely expensive, the literature cites 0.2 USD/mg of protein for antibodies, which already have a purification process which has been refined since the nineties. A dress weights 120.000-350.000 milligrams, that would make a dress cost 70.000 USD. Way too much for anyone to pay for clothes. A mg of an antibody sells for >200 USD, in that technology the 0.2 USD/mg purification cost is negligible, but for large-scale protein production it is prohibitive. Most likely they are struck with the purification.
Most protein purification methods were designed for the pharmaceutical industry, where a mg of protein sell for hundreds of dollars, but they are totally unsuitable to produce silk proteins for clothing.
