are made with a panel seat that has two seams running on the outer edges of the back seating area, creating a center rear panel. Most mass-produced commercial boxer shorts are made using this design. Two less common forms of boxer shorts are "gripper" boxers and "yoke front" boxers. Gripper boxers have an elastic waistband like regular boxers but have snaps, usually 3, on the fly and on the waistband so that they open up completely. Yoke front boxers are similar to gripper boxers in that the wide waistband yoke can be opened up completely, and the yoke usually has three snaps to close it while the fly itself, below, has no closure mechanism. There are two types of yoke boxers: one in which there is a short piece of elastic on each side of the waistband which snugs up the yoke to fit the waist; and "tie-sides" which have narrow cloth tapes on each side of the waist yoke, like strings, which are tightened and knotted by the wearer to make an exact fit. This style of underpant was very common during World War II, when the rubber needed for elastic waistbands had to be used for military purposes. Boxer shorts are available in white and solid colors including pastels, and come in a variety of patterns and prints as well; Traditional patterns include "geometrics" (small repeating geometric designs), plaids and vertical stripes. Additionally, there are innumerable "novelty" boxer short patterns. Boxer shorts are produced using various fabrics including all cotton, cotton/polyester blends, jersey knits, satin, and silk. Fertility Some studies have suggested that tight underpants (like briefs) and high temperature are not optimally conductive for sperm production. The testicles are outside the body for cooling because they operate for sperm production at a slightly lower temperature than the rest of the body, and boxer shorts allow the testicles to operate within the required temperature range. The compression of the genitals in briefs, boxer briefs, or thongs may cause the temperature to rise and sperm production to fall. There is a similar theory regarding testicular cancer risk. Other sources dispute this theory. A study in the October 1998 Journal of Urology, for example, concluded that underwear type is unlikely to have a significant effect on male fertility. Boxer shorts for women Boxer shorts for women have come onto the market in recent years. They are often worn as loungewear.