Soul Cycle Mothership, a molded fiberglass speaker cabinet for bicycles.

Step 8 Apply mold release, then paint your shape with flexible moldmaking polyurethane rubber.

Build thin coats up until you have a 1/4" - 1/2" thick mask. You paint the sticky liquid rubber on the shape, about 1/16" at a time. Many coats are required. The liquid rubber I used mixes by volume. Part A was the consistency of light honey. Part B was the consistency of creamy peanut butter. Getting equal volume is difficult with the the Part B, because when you try to put it in a cup, the voids are huge and it's impossible to measure the volume accurately. I ended up eyeballing it, which I do not recommend, because certain layers in my mold did not fully cure. In other words, I know that the longevity of this mold has been reduced by not getting accurate 1:1 by volume mixes. Next time I'd probably find what the weight ratio is and then use a scale to get 1:1 mixes.