They have both. We have a white daybed that we originally bought the chipboard version of, but the package was damaged and returned and they had none left, so we got a slightly different, also white, one in wood. I think it was pine.
Chipboard is not always worse though. Soft/cheap wood can be weaker and warp more easily than chipboard, which is mainly glue. Depends on the quality of the chipboard maybe - some of that stuff is strong and like plastic - some is closer to compacted cardboard.
Ikea furniture is kind of like the lottery, you win some you lose some. Some of their stuff is amazing and lasts forever - some of it will fall apart when you look at it. You can probably tell which is which by going to the store and banging it about a bit to see if it's sturdy.
ETA. Yep - I have a single bed - now kept as a spare - that is about 25 years old and sturdy as ever. My mirror cabinet is 15 years old and looks like the day we bought it... for less than just a straight mirror cost anywhere else!
On the flipside, the day bed we bought and returned was rubbish.
We got some really solid little kids chairs 2 years ago that are so sturdy that DH or I can sit on them WITH a child on our lap - but they don't have them anymore.
Edited by CallMeAliG, 15 January 2013 - 10:29 AM.