Breg Cotton Knee Brace Undersleeve Breg Cotton Knee Brace Undersleeve. Cotton undersleeve has closed patella (Cotton/Lycra blend - no elastic). Prevent skin irritation and brace movement. Cool, breathable material. Length is 19" long for all sizes. Can be used with all Breg Ligament or OA Knee Braces. Easy to use, slip-on style undersleeve. Durable and easy to wash material.