Water absorbent resin particles

Water-absorbent resin particles comprising:

• a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer including at least one compound selected from the group consisting of (meth)acrylic acid and a salt thereof,
• wherein a proportion of (meth)acrylic acid and a salt thereof is 70 to 100 mol % with respect to a total amount of monomer units in the crosslinked polymer, and
• a dissolved content in an aqueous solution of 0.9% by mass NaCl at 25° C. is 10% by mass or more and 25% by mass or less, and a dissolved content in an aqueous solution of 0.9% by mass NaCl at 40° C. is 14% by mass or more and 30% by mass or less, where the dissolved contents are measured by the following dissolved content measurement method which is performed as follows:
• 500 g of an aqueous solution of 0.9% by mass NaCl put into a 500 mL beaker is adjusted to a temperature of 25° C. or 40° C. and stirred at 600 rpm,
• 2 g of the water-absorbent resin particles is put into the beaker, stirred for 3 hours, and then filtered through a 75 μm JIS standard sieve, and a filtrate is recovered,
• the obtained filtrate is further suction-filtered using a type 6 filter paper defined in JIS P 3801,
• 80 g of the filtrate obtained by suction filtration is weighed into a pre-weighed 100 mL beaker and dried with a hot air dryer at 140° C. for 15 hours, and a mass (Wa) of a solid content of the filtrate is measured, and
• a mass (Wb) of a solid content of a filtrate is measured in the same procedure without using the water-absorbent resin particles, and a dissolved content is calculated by the following formula,
• dissolved content (% by mass)=[((Wa−Wb)/80)×500/2]×100.