After receiving lots of helpful tips in this thread I decided on a set of Innovation Polychrome 140P for my Chadwick folding. Here are some comparisons with Spirocore Red and Innovation Ultra Black after having them settle for about 15 mins. Arco tone: The Polychromes have a wonderful tone with a woody character. Red Spiros growl more, almost sounding harsh in comparison. (The Ultra Blacks can be bowed with a generous helping of rosin but it's hard to start the tone with a bow.) Arco feeling: Polychromes are medium tension and the other strings have high tension. This makes the string significantly easier to start and control than the red Spiros (please note that I'm quite a newb on arco). Pizz tone: Very sweet and balanced tone, will probably work well in most contexts. Ultra Blacks are thumpier with a less elaborate tone, while the red Spiros sound balanced but with slightly longer sustain and a bit more bass guitar character. Pizz feeling: The Polychromes are easier on the hands without feeling floppy. The D string is the least "unfloppy" but it's not a problem while playing. Very easy to pluck and with good slap control. Haven't tried drag slaps yet but I expect it will be easier than on the Spiros or Ultra Blacks due to the lower tension. Other: No setup changes were needed going from red Spiros. The bridge notch for the E string may need widening but it's a close call. The Polychromes are not as smooth as the other strings – I can feel the windings on the lower strings in glissandos – but they are by no means rough. Conclusion: Polychromes were a notable step upwards for me from the red Spiros and is equal or better in all areas. I play mostly bluegrass and some jazz, and spend most of my practise time with arco and Simandl. I had hoped for a good mix of UB and red Spiros and this string delivers it. Time will tell if wear from tearing down/setting up a folding bass will impact the lifetime.