A Mattress is Bedding material compacted to 3 to 4 inches and sandwiched in a heavyweight polypropolene or other fabric. Possible fillers include: long or chopped straw, poor quality hay, sawdust, shavings, rice hulls and, most commonly, shredded rubber.

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Other /More definition:
A Mattress is Bedding material compacted to 3 to 4 inches and sandwiched in a heavyweight polypropolene or other fabric. Possible fillers include: long or chopped straw, poor quality hay, sawdust, shavings, rice hulls and, most commonly, shredded rubber.