
I prefer the pads for the same reason as stated before,I could place it at one end of the bed, they can climb on and off the pad, sometimes Mum and all the pups were on the pad, pups were on the pad alone or no one was on the pad and the pups must have been warm enough as there was no puppy pile they were scattered around the bed.
I have rice Mummas too,popsocks[2 layers each] filled with rice which can be warmed in the microwave and used for emergency vet trips[touch wood never used], can be shaped around pups/Mum as required.