I mean, I've heard Acrylic is easier to insert and take back out, possibly some clarity advantages from the more rigid structure, more durable for long-term ownership, and easier to make with special/unusual color designs,
But I've heard Silicon is more comfortable due to it's flexibility, CustomArt and a few others have really pushed the bar with more complex art, less bass resonance, comfort, better sound isolation and easier to get a good seal, comfortable, and is less sensitive to contact microphonics (rubbing sound in your ear), and more comfortable to wear.
I know I know, but seriously, I've heard of people wearing either CIEM material all-day or falling asleep with them on, so there must be a lot to the custom shape. I personally ordered a CA silicon for myself, but I haven't owned a CIEM yet.
But I've heard Silicon is more comfortable due to it's flexibility, CustomArt and a few others have really pushed the bar with more complex art, less bass resonance, comfort, better sound isolation and easier to get a good seal, comfortable, and is less sensitive to contact microphonics (rubbing sound in your ear), and more comfortable to wear.
I know I know, but seriously, I've heard of people wearing either CIEM material all-day or falling asleep with them on, so there must be a lot to the custom shape. I personally ordered a CA silicon for myself, but I haven't owned a CIEM yet.