Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: what are the length of this bolster?
Document: This bolster is a nice product with firmness and density - I recommend it for use on a daybed or as a headrest on a twin bed - two are the exact length of a twin mattress, one is the exact width. I ordered two and when I opened the box there was a slight smell of petroleum as many foam products have - I aired them out for a few days before putting on the bolster covers and the smell went away.
The bolster is truely firm. That is what I needed. If I need more I plan to buy this product again.
These bolster fillers are great. Solid stuffes for any pillow. Terrific to lean against in lieu of a headboard. Would definitely buy again.
Very good product. I read the reviews before ordering and was not sure about the &#34;rock hard&#34; firmness. It is Extra Firm not that bad. It stays in shape behind my back just how I wanted it to be. I ordered two for in-bed reading and they fit Cal-King bed perfectly.
This has served as an alternative headboard and the extra firm support makes it great for leaning against when reading a book.
These are perfect for a daybed if you want a very firm backrest. The foam looks to be high quality.
It was just what I wanted and it was shipped and received quickly. I had not been able to find them. All I can say is fantastic.
I went to the spa and this is what they used during my pregnancy massage. I was so comfortable that I'm ordering one for home use. I need better sleep positions and I really think this is going to help me out. At least afterwards, I can use it for other stuff as well (backrest when on my laptop, whatever).
I use this as only the back base for a day bed - it is no where near wide enough to serve alone as the back if you want to sit on the bed as a couch. The bottom width of the wedge is 8.5 inches deep. So if you have a small twin sized bed, you need to add a really deep cushion to make the bed into a sitting area. It works for me because I found some really nice big cushions that I lean against this base wedge.
I recently made a built-in daybed, and ordered two of these cushions. I chose extra-firm because I did not want them to be too soft. Please note that Extra Firm is the same as ROCK HARD! I doubt that anyone would really want a cushion  that is as hard as this one.Our solution was to add LARGE soft pillows, as another reviewer has mentioned. Purchasing "extra firm" for a daybed, and adding an assortment of soft pillows, has worked out great.
Answer: 36"