Here's what I did...it's a bit different from what other posters recommend, but it worked great for me, and I'll do it again!

I used Always maxi (with wings, but the wings aren't important, I just don't think I found them without wings) for Plus sizes. They are a bit longer and wider than the regular ones. They do have the locking core or whatever, but IMO, that's what made them work best--kept them from feeling soggy/drippy, but I still had the cold therapy.
Anyway, I made up a strong "tea" using a blend of herbs (I got mine from my midwife, but you can find lots of different herbal sitz baths or recipes to make your own from bulk herbs, etc. Wish Garden has a nice one). I strained out the herbs and then saturated the pads. You can use a turkey baster, or a large medicine syringe...I actually used a clean "booger-sucker" (nasal bulb)!

I saturated the pads pretty well...at least a couple Tbsp per pad. Then place them on a cookie sheet, turned on their sides and curved into a "C" shape. Freeze until hard, then transfer to a large ziploc bag.
Be sure to label them, so your husband doesn't--for some strange reason--mistake them for fish fillets and start to thaw them for dinner!

I don't know if they are really very absorbent, because I only used them as ice pads, either inside Depends (for the first couple of days) or with a larger post-partum pad or prefold under them, to absorb the actual blood.
Anyway, YMMV, but that's just what worked for me, and they were awesome! I made up at least 18 of them, and I loved that I could have as many as I wanted, as often as I wanted, instead of having to ration the expensive ones. HTH!
