I've been raising and releasing butterflies and moths for about five years. Got my feet wet with common butterflies like Queens, Monarchs and Gulf Fritillaries but for the past few years I've concentrated on raising the uncommon and rare butterflies when I can.
Have used a variety of containers over the years but starting making my own using everything from plastic trash canisters to food storage containers to store bought reptariums.
The only medium I'll use to keep larval host plant cuttings moist and fresh is wet floral foam. Most times I don't cover it - just brush off the frash when I clean out the containers or replace the piece with a new one. When I raise piggies like Monarchs and Queens that eat and poop I'll use saran wrap to keep it clean.
I highly recommend using wet floral foam instead of putting cuttings in a jar with water. Caterpillars will crawl up and down plant stems and they will fall into the water and drown! There is no way they can hurt themselves when you use the wet floral foam.
Wet floral foam can be purchased at Walmart or any craft/hobby store. I buy it in three packs and cut the blocks into the size or shape I need.
Photos of wet floral foam. I use jar lids, old pill bottles, dog food tins, pretty much whatever I can find that suits my liking.
You can either pour water onto the wet floral foam piece or drop it into a dish of water and let it soak up all the water it can. You can also add more water each day or every other day to keep the foam wet and the cuttings moist.