Passive IEMs are better, ANC is always weaker and more selective. I was once using Etymotic IEM and frantically searched for the source of a loud wind noise that hit my ears upon removing the earphones, only to realize it's just an air conditioner on the ceiling. That don't happen with ANC headphones, partly due to technology and partly for product safety concerns.

Have you compared passive IEMs to Apple's noise cancelling headphones? I compared Apple's products to properly inserted earplugs and Apple's ANC was better for low to medium frequency sound, so I wonder how you arrived at the opposite conclusion when it comes to IEMs

With properly inserted hardcore isolating earphones, and with music playing at low volume(important), I just don’t notice any other sound. Including landline ringing. Perhaps fire alarms too. It’s an auditory anesthesia. Like if I’ve put on a VR goggle, but for my ears.

And that is natural, after all it’s 40dB advertised isolation with ~15dB? sound on top. There’s no way those ANC earphones with small drivers powered from a toothpick batteries and thin rubber cap sealing the ear canal can beat that.

I also have a SONY WF-1000X, and an SE215 for that matter, both with Comply tips. They are nice, but no match against proper Etymotic dead silence.

I trust you, I'd like to delve a bit deeper into why this is the outcome to understand it better.

I hear people sometimes use Etymotics with Comply tips. Wouldn't that create the same seal as using WF-1000X with Comply tips?

Also do you have a recommendation of an Etymotic IEM model plus a tip I can try for maximum effect

ANC earphones are not designed with maximum sealing in mind(sometimes intentionally). Doesn't matter how plug and ear canal is tightly fit together, if what is suspended in the middle was a pipe with open ends.

ER4SR is the most classic/standard Etymotic model currently sold, other models complementing in both direction of prices. Perhaps more important than tip selection is correct insertion, or Practice and patience, which is unbelievably the exact wording used in their instruction manuals at least for my ER-6i. It is definitely not the healthiest earphones in the market.

What do you think of IEM silicon tips that are custom made for your ears, in order to improve the passive noise blocking? Unnecessary?

Pretty good, I use Shure IEMs to block wind noise on motorcycle rides and having access to podcasts/audiobooks are a nice bonus when slogging down freeways. I can still hear car engines and sirens, but it removes the wind buffeting in my helmet that really drains you (and damages your hearing) on a long ride.

Better, in my experience. They can get around 25-30db reduction across the spectrum, and they don't let voices (i.e. non-repetitive noises) through like ANC can.

Combine them - I often wear earplugs plus a pair of bose nc700s. They have better noise canceling for your conditioner noise compared to my airpod Max's

They are definitely better. ANC can't beat physically blocking the soundwaves from hitting your eardrums.

Is this based on your experience having tried both? Because that reasoning is questionable. IEMs don't block all sound from hitting your eardrum, some of that sound will hit your eardrum via bone conduction. And ANC headphones do block some sound passively, the inner ear ANCs can often create an airtight seal.

Yes, I have tried both. However the only ANC I have experience with is AirPods Pro, so that's all I have to go on. But I can definitely say that IEMs do a better job than the AirPods.

Which IEM and tip did you get? Do you know why the IEM was better given that the Airpods Pro also plugs the canal?

Shure SE215 and the default tip it comes with. I can only speculate on why the IEM is better, but I suspect it comes down to the tip material creating a better, more substantial seal. The outer shell is also physically larger, and that may also play a role in keeping more sound out.

I wonder if we can replace the tip on the Airpods Pro to create and IEM like seal. I suppose that should be the best of both worlds? But the outer shell would still be smaller so maybe not.