The other issue with the hollow bars is that if enough weight was placed on a spot they would begin to bend. The issue became so bad that a 90 day warranty was put in place by most manufacturers of these frames. Another issue the black metal frames suffered from were bending stretcher bars or rails. Again the hollow nature of these strecther rails presented issues with breakage and bending.
Secondly, it should be borne in mind that it isnt the futon frame that provides the comfort when either sitting or sleeping on a futon: it is the futon mattress that provides the comfort. A futon bed mattress made for a tri-fold futon frame is not as thick as that for a bi-fold futon bed frame. Therefore, if you intend to sleep on your futon regularly you might be best to buy a bi-fold futon bed mattress: a thicker mattress tends to provide more support.
However a futon bed mattress made from cotton and polyester is quite flexible. A futon mattress made from 100% polyester is by far the lightest of all; it also rates well for firmness and rigidity. A futon bed mattress made using inner springs is by far the heaviest and would only be used when the futon is almost always used as a bed. As you might expect, the rigidity of a futon mattress using inner springs is excellent.
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