Code is an R-13 in 2x4 exterior walls and R-19 in 2x6 walls Batts are pre-fitted for the stud cavity unlike rolled insulation Basic insulation package. Manufacturers now produce medium- and high-density fiberglass batt insulation products that have slightly higher R-values than previous varieties. The denser products are intended for insulating areas with limited cavity space, such as cathedral ceilings. High-density fiberglass batts for a 2 × 4 inch (51 × 102 millimeter [mm]) stud-framed wall has an R-15 value, compared to R-11 for "low density" types. A medium-density batt offers R-13 for the same space. High-density batts for a 2 × 6 inch (51 × 152 mm) frame wall offer R-21. High-density batts for an 8.5 inch (216 mm) spaces offer about an R-30 value. R-38 for 12 inch (304 mm) spaces is also available. One unconventional fibrous insulation product combines two types of glass, which are fused together. As the two materials cool during manufacturing, they form random curls of material. This material is less irritating and possibly safer to work with. It also requires no chemical binder to hold the batts together, and the material even comes in a perforated plastic sleeve to assist in handling.