Early designs involved a steel tooth design that would fit into pocket welds on the arms. These would snap off over use. The alternative design was to run a bolt through the arms and into the rails. While better it still did not address the issue of bending stretcher rails. Bent hinges also added another issue that would happen from use over time. While not as common as the other problems this issue still led to the failure of many black metal frames.
But if space is at a premium and you will only occasionally sleep on your futon best, than the tri-fold will certainly suffice. The best futon bed mattress is the one that best suits your requirements. Consider the space you have available, and what will be the main function of the futon bed mattress. If the futon is going to be used regularly for sleeping on, then most consumer reviews of futon beds tend to favour the bi-fold futon frame and mattress.
The flexibility of an inner spring futon mattress is quite poor, but you would only really buy this type of mattress if the futon is going to be used as a bed most of the time. Futon beds are a popular choice for many consumers due to their flexibility of function. Before buying a top rated futon bed mattress make sure that the qualities - mentioned above - of the mattress are what you require. If you know exactly what you want before you buy you are going to avoid being disappointed with the purchase of your futon bed.
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