Any plastic in the junk mail (window envelope, plastic cards, gummy stuff used to stick cards to paper etc) will not decompose and will need to eventually be sifted out. Any plastic emulsion coated paper (shiny type paper as in magazines) are meant to be somewhat more water resistant will not easily breakdown completely to be consumed by the worms. Most inks used today are food safe however there may still be some bright reds-oranges-yellows that use cadmium, however with the quantities being so tiny I wouldn't worry, and the other minerals should be quite safe (titanium, iron oxides, cobalt, etc). You should be able to run corrugated cardboard through your shredder without issue. I've been using our 10+year old Aurora 5-sheet shredder for the last couple months and it makes excellent worm bedding out of all our cardboard boxes. I've learned to not mix shredded paper with the wet castings but instead just lay it on top (in a 6" layer) and let it slowly soak in the moisture from the humidity beneath and the worms will enter the shredded paper/cardboard layer on their own terms and slowly turn it into castings... you just keep adding more shredded cardboard to the top and that way the stuff below will never mat down into clumps.

Some do but I dont shred junk mail for worms. I do confetti shreds to mix in with new bedding but I manually long strip for a covering layer over bedding and food scraps. I dont like the confetti on top as its too hard to move around to check on food matter and worms.

Very helpful comments, thanks. I do always double-sift the contents of the old bin when I sort out the worms and put them into new bedding, first through a sifter I made with 1/4-inch hardware cloth (stuff too big to go though that is recycled into the new bin), and then using a sifter with screening. That gives me a final check for stray tiny worms (and cocoons) and also gets out the roly-polys and some - but of course nowhere close to all - of the millipedes. The bulk of my bedding is usually finely-chopped leaves gathered in the fall, but I did not remember to bring enough indoors last year.

I like the idea of shredding cardboard. The brown of it is more natural and appealing to me than the white paper, even newspaper. So since I have some boxes still left over from Christmas shopping, that is what I will use.

Me thinks removing (before shredding) those things that simply won't decompose including staples and other things mentioned by monomer is by far easier than sifting those items later.

Simply, cut or tear the envelope in half then shred the part w/o the window. IF you must use the window portion it is much easier to remove when it is NOT shredded.

In some towns there are FREE advertising newspapers. Many stores also have FREE cardboard boxes.

I prefer the cross-cut shredders. Sometimes you can get papers shredded at the office but that will almost always contain all the things mentioned above that will not decompose (and more).

I always remove staples (hard on the shredder blades, I figure) as well as plastic envelope windows prior to shredding.

You do need to be watchfull of what you put in your bins. I scrap all flyers that come in the papers and I also dont add junk mail . If you put junk mail in your will find things like tape , plastic windows in your vc at compost, worms cannot compost it. Also if you shred credit cards and forget about it later after adding to the bin you will find those bits of cards in the bin as the colors will show up. You will say WTF is that then you remember.

Nice video... let me add a couple thoughts if I might... corrugated cardboard is merely three sheets of craft paper glued together. I would say nearly all paper shredders should be able to shred three sheets of craft paper... heck running a paper grocery sack through a shredder can be far more demanding (if you don't cut the bottom out separately but instead leave it folded then low power shredders will struggle with it... like my cheapy 5 sheet Aurora). Just be aware that there are different strengths of cardboard used for shipping boxes (I had to do a Google search to learn about the different classifications)... most are easy to shred however some boxes designed for shipping big heavy items such as electronics, subwoofers or gym equipment will be a lot harder on your shredder (as the craft paper used is a much thicker stock and of a stiffer formulation)... still even my cheapy shredder can shred this high-strength cardboard IF I pre-cut it into thin enough strips. Thus leads me to another suggestion.... get a paper cutter. I have an 18" German made paper cutter (self-sharpening blade) and can cut up a typical Amazon box into strips in less than a minute... actually pre-removing the shipping labels and packing tape takes longer to do than actually cutting up the box. For most typical cardboard a 6-8" wide strip is no problem for even my humble lowly powered shredder to handle... for stouter (high-strength) cardboard I may have to cut it down to 3-4" widths to keep from bogging down the motor too much or completely stalling it in cases. The only issue preventing corrugated cardboard from being run through a paper shredder would be the access slot of your particular paper shredder.... I've noticed on some newer shredders the slot appear rather narrow or on some limited to a funny angle.

Also I would be very cautious about running "chip-board" through a shredder.... I believe that's the term (hobby-crafters) used for basically packaging cardboard like cereal or tissue or shoe boxes. Those can actually be a lot harder on the shredder blades than corrugated cardboard if its thicker or doubled over, some of that stuff I wouldn't even attempt to run through my shredder at least.

Final thoughts... I will reiterate, if the dry paper shreds are simply layered on top of the moist bedding/castings rather than mixed into the top layer, it will not actually clump... yes, it helps to have some cardboard shreds mixed in. Moisture slowly wicks upward into the shreds that is in direct contact thereby softening it and holding in a high humidity environment and the worms will migrate into this portion of the layer and the microbes they bring with them begin the composting process... without any of the paper clumping. I've only discovered this recently (a month) and its working out quite well. No leachate, no clumps, no escapes, and no more fluffing the bedding/castings... I just pull back the shredded layer (I use paper and cardboard... simply depends upon whatever I'm "recycling" at the moment) spread the food down and replace the paper layer, that's it.

Oh and in case someone reading doesn't know about oiling paper shredders... think of it as necessary periodic maintenance that must be done to keep down the dust that shredding paper and cardboard creates, this can lead to dull blades and tends to get compacted into the blades eventually causing binding of the motor and overheating issues, basically killing your shredder before its time. To oil a paper shredder you simply take a couple sheets of printer paper and smear vegetable oil (yes it must be a vegetable based oil) over both sides until its saturated then allow it to sit for a few minutes and run this oiled-paper through your shredder... do this at least once a month and your shredder should last a long time.

As far as shredding cardboard yes I agree with the above commentor. The Aurora is fine for paper but will bog down and eventually stop if you try cardboard. However pay just a little more and get a Fellowes either 10wc or w11c both will handle it well and they have the 5.5 L basket compared to the 3.75 basket of the aurora. I have recently sold my 10w c but it continued to work fine, I shredded an entire box 4' x 2' cut up small enough for the entry, no problem. Using the W11C it hardly slows when inserting cardboard and love the basket size. The above hint on the oiled paper sounds like a good one and should be done on occasion especially on a good shredder.

The particular Aurora model I am using is very old... my wife bought it for me maybe 15 years ago? I tried looking it up online and it appears they quit making that model at least 12 years ago. It is quite basic, the unit sits on top of a waste basket and it is rated for 5 sheets. I believe at the time it cost around $20. I've had my eye on several newer, more powerful paper shredders for awhile now (Amazon Basics seems to make a good one) and have just been waiting for this one to die, a few months ago I thought perhaps running cardboard through it would speed up its demise... so far, it continues to run just as good as it always has... it just keeps on going and going and going and...

Yesterday I shredded up 4 of those huge leaf-collection bags I had gotten in the fall full of shredded leaves from a friend who knows I use them in my garden. I recalled that I had used the leaves to mulch my raised beds over winter and left the empty bags to dry out thoroughly in the shed. So I went out & fetched them in, cut them into strips that fit thru the shredder & went at it. Got enough to prepare another new bin - yay!

I next mixed this brown paper confetti with the un-digested leftovers that I sifted out of the old bin as I sorted out the worms, as well as with about a gallon of shredded leaves I had had in the basement and have watered it all down. I also always save & dry all my eggshells & grind them to powder in an old blender - mostly to use in the garden when I am planting my tomatoes, but I will mix in some of that into the new bin as well. I have used the powdered eggshell in the past & they seem to like it. :-)

Thanks to all of you for your suggestions!