Has any one used these with Flip diaper covers? If so, did you like them?

I don't know about Flips but I have used them with Rumparooz, econobum, Nikki's diapers, gDiapers, and Earthwise and they fit all of those. So they will probably fit yours too. I don't have a ton of exposure to other inserts, but the ones I do use, I like these best. And the color hides all stains, they don't really shrink either. Hope this helps.

Most diaper liner brands on amazon “claim” their liners are flushable however we at Natutally Nature recommend you do not flush bamboo liners. Look at Grovia diaper liner reviews. A customer left pictures of what their liners did to his sewer system. Naturally Nature’s liners are Biodegradable however we feel best practice is to compost and not flush. All other liner companies are not being truthful about the ability to flush these. We are the only liner brand that recommends not flushing. Please take time and read the reviews and look at customer images on Grovia.

What are the wash/dry instructions for these?

I believe the instructions came in the package with them. I do not want to give you false information, however, after the initial washings before use, I wash them exactly as I do the diapers. For the diapers, you wash in hot water, but you're not supposed to use softeners or bleach, which I believe is the same for the inserts. The inserts do require 3-4 washes prior to use in hot water and then you dry them. I use my dryer for that, however, you can hang dry them if you are more comfortable with that. Have you tried searching for the washing instructions in your browsers search engine or looking at the company website?

Do these work well with Bumgenius 4.0 diapers? Would I have to fold them over like I do with the inserts they came with? (My baby is 3.5 months)

Real bamboo inserts (instead of microfiber wrapped in fleece like these are) will work better. These have tons of bulk but not much absorption compared to inserts where all the layers are natural fibers