Can’t say anything interesting about soundproofing, but I did invest 3 years trying out every possible earplug out there and I can give you a quick summary:

• pvc foam plugs
  • pros
    • by far the most effective option at overall noise reduction
    • do not amplify your own voice when speaking
    • widely available
  • cons
    • hard/annoying to apply, especially in hot environments
    • ineffective when applied incorrectly (watch a video or two, it is not obvious)
    • single use, making it both environmentally problematic and costly in the long term
• custom molded silicon plugs
  • pros
    • easy to put in
    • comfortable even for long usage
    • custom acoustic profile for musicians
    • about as much noise reduction as possible except for pvc foam (still a significant gap between them)
    • long lasting when cleaned and stored properly
  • cons
    • really expensive
    • need to go get your ear scanned/molded
    • the plugs are physically large making it slightly less portable (if you have small pockets or really tight jeans)
• custom diy molded plugs
  • pros
    • inexpansive
    • noise reduction comparable to proper custom plugs
    • comfortable
    • easy to put in
    • no need for an appointment
  • cons
    • many of the ones on the market are made of porous materials, making them uncleanable overtime so they are not actually safe for long term reuse
    • physically large so less portable
• silicone / rubber plugs
  • pros
    • cheap
    • widely available
    • large variety of shapes and sizes means that you can find ones that will fit you well
    • cleanable and reusable
    • good noise reduction
  • cons
    • not as good at noise reduction as custom plugs
    • need to be replaced about every year
    • can be uncomfortable for long periods of usage
    • often odd shapes are marketed as better, all shapes perform basically the same so ignore it.
• wax plugs
  • pros
    • block water from entering you ears when swimming
  • cons
    • low noise reduction as they are not really meant for that
• filter based adjustable plugs
  • pros
    • about the same noise reduction as silicone plugs
    • reusable
    • good ones will be easy to adjust making them really versatile (can be used in different noise levels while being able to hear and not be too insulated from the environment)
    • cheap, about 2-5 times the price of silicone ones
    • easy to put in
    • comfortable
  • cons
    • can break
    • sensitive to dust
    • not easy to find

This basically covers it. My personal setup is a small two chamber box that is always with me, in one chamber there are pvc foam plugs for max noise reduction and in the other chamber I have adjustable plugs that have 3 levels that I would define as:

1. Everything is slightly quiter, nice for slightly noisy places where I still want to hear or have a conversation
2. Not used often, but can be useful in some specific noise levels where I want some quite but have to still be aware
3. About as good as silicone plugs, I use it almost daily whenever I want some quite (basically anytime I walk in the city)

If you are interested, I am using 3m foam plugs and these random adjustable plugs that I found that are surprisingly good quality for the price (cheap so don’t expect anything special)

https://www.aliexpress.com/item/1005010386481009.html