Fleece in a non c and c cage?

i am wondering if fleece is going to work as well in a pet store cage as it does in a c and c cage, i know obviously it wont by the same but i would like to hear some personal experiences. and i cant get a c and c cage because i have a outside cat that likes to bring us little rodent presents every now and then and i dont think having a open guinea pig would be very smart