Abstract: Method for producing Fiber insulation batts suitable for building thermal insulating applications are made using polymer fibers such as PET. A mixture of staple fibers and binder fibers are used to make the batt. The batt has a bulk density of 6-14 kg/m3, a thermal conductivity of 35-50 mW/m-K and a lambda*density value of from 250-550. The batts can be made by forming a web of the fibers, and calibrating and heat-setting the web. The web can be formed using pneumatic or mechanical carding processes. In some processes, the batt can be made by forming a stack of multiple plies of the web and calibrating and heat-setting the stack.