Why not make them out of MDF? no splinters!

What about painted pine? Cheap, easy to fit to custom sizes. Although it would need painting.

Did you talk to the Elfa trained folks at Container Store? They will cut their wire shelves to any length included in the cost. If you are concerned about things falling through the grate, they also have shelf liners to sit atop the wire shelves.

I'm with your husband - use the plywood cut to size mounted on some simple 1x2 wooden cleats bolted to the sides and back wall into the studs and sand/paint the whole thing.

Otherwise, you could get some of those 12" deep melamine shelves and mount them back-to-back on those same 1x2 cleats - but plywood will hold more weight than particleboard/melamine shelves.

Why not lay two 12" shelves side by side? Just double up on your brackets.

I went to Ace hardware in Cole Valley they cut shelves for my closet to my specs. They are plywood and holding quite a few heavy containers.

Cover plywood or MDF with pretty fabric. You can use fun patterns found in the remnants section - mix it up to match that great red you have painted in there.

I just redid my bdrm closet with ELFA from the Container Store. They cut all the shelves to size, you don't need to worry about them not fitting. Hurry, 30% off all ELFA until Feb 9th!

Priscilla's idea would be my first choice - double up 12" shelves!

Put two 12" deep shelves on cleats, which means that if you ever need one shelf to be shallower (so it's easier to reach the back of it, for instance), it's a simple matter of removing the extra plank.

I just cleaned out my linen closet (about the same size as yours) and realized that having super-deep shelves for towels didn't make sense--there were always towels piled up in the back that never got used. With 12" shelves, all the towels are within easy reach, and I can get inside the closet a bit, which makes reaching the highest shelves much easier.

My apartment has very deep shelves in the linen closet, and as a petite woman, they are very difficult for me to access. I would prefer to have shallow shelves so every towel, blanket ect. is in my reach.

I also find, like Bobbini, that I have towels piled in the back that are never used. Because they are not in the regular laundry rotation, the colors are now slightly different than their oft-used brethren.

The shallow shelves, with room to walk into the closet a bit seems lovely to me.

interesting comments on keeping the shelves shallow. I'll have to think about that one!

I wasn't considering MDF because the one plank I saw at Home Depot had a giant "this product contains chemicals that may cause cancer" on it. Being 9 months pregnant and all, I didn't feel like taking a chance.

By the way, since I submitted the question I came across two more possible answers but unfortunately neither works for me:
-one can buy deep (20"?) melamine shelves at ikea upto 39" width (too short for me)
-container store also has a different line called "skandia" which is what their own inventory is stored on. But each shelf was $30 and again did not fit my size requirements.

I guess plywood is the way to go for now!

Don't do it! You do not want deep shelves in that closet. As the previous commenters have stated, things in the back will be LOST FOREVER!

Instead, get 14" shelves and mount hooks on the space on the sides to hang things like winter blankets, that you won't be taking in and out regularly.

Try Lowe's and look near the kitchen/garage cabinets for white melamine countertops to lay on top of cabinets. We found some shelving to go on top of two file cabinets for a desk that was at least 20" wide and either 48" or 60" long for about $20-25 per shelf. I think they'll cut it for you.

"this product contains chemicals that may cause cancer"

That's a warning not to eat it. Ask you husband to mount them so that you are not the one handling them, and you should be fine. You could also ask your husband to cover them with contact paper so you don't ever touch them.

Oh, and melamine shelves are MDF covered in melamine.

I'd stick with shallow shelves chosen or cut to match the depth of a folded towel. It's true that deep shelves lead to disorder. This leaves room in the front of the closet to keep your vacuum cleaner in there, or a big basket or bin (on wheels?) of oversized items like comforters. And it helps avoid the feeling that your closet is going to burst when you open the door.

... that wasn't clear, was it? The basket/bin(s) would roll under the bottom shelf, if you did not run shelves all the way to the floor.

I actually have shelves in my linen closet that are made with two 12" wide boards, just as others have suggested. I took out a couple of boards at around eye level to make some of the shelves shallower.

I have shelves that are 1" thick birch plywood, cut to order by the lumber supplier. I got the iron-on edge tape from Home Depot and ironed it on myself. I then sprayed a couple of thin coats of urethane to seal everything and mounted them on 2"x1" cleats. The naturally light birch color might look fine with the color of your closet, and if you lightly sand the edges you won't have splinters.

Don't have an opinion on shelf depth. Mine are all no more than 22", and not a problem.

I just recently did my linen closet at the container store because they are doing their 30% off sale right now. What's really awesome about is is that they will cut your shelves for free to any size you need to fit. Plus the display at their store showed a tiered linen closet, which works perfectly for all my differently sized items from blankets to towels and sheets (they have these vertical dividers that I can move around on the shelves to divide different items). What's really awesome is that it's really easy to change out the parts and move the shelves too, so if you ever wanted to change the closet's purpose it would be a simple job to do requiring no tools. In addition, their system only required about five or six screws for my four foot closet, making it super easy to install.