thanks for you help, i'll try to clarify things.
when i wrote hostel- i meant youth hostel-albergue juvenil....the cheapest way to stay in spain. (well-sort of).
the reason i posted this was because of the mixed messages i got from other sites, and this one. i've heard, as i mentioned, that some albergues do not allow sleeping bags.... but i'm not sure if that is a rumor or truth, for it isn't posted on any rule page of any hostel association i've seen.
i like to have more than a thin sheet on me when i sleep, so that is why i was thinking of bringing a sleeping bag-and in case i decide to travel north and stay somewhere somewhat cool.
so then, is it a general ruel in albergues to not allow sleeping bags?(i dont' want to pay any sort of fee -i've read that at times there is one) to rent sheets or extra sheets. but i also dont' want o be carrying around any excess luggage either.