Grub's Ptarmigan 5.0 Lace Up Field BootsThe Grub's PTARMIGAN 5. 0 Lace Up Ankle Boot is fantastic for general activities all year round thanks to the 5MM INSUFOAM ULTRA combined with the SUPERDRI lining. The 6mm NITROCELL footbed is an integral part of the insulation package, while also providing excellent comfort. While the VIBRAM multi sport outsole gives you superior grip on all surfaces and on higher grounds. Lace Up Ankle Boot Comfort Rating: +20C to 20C VIBRAM Bristol Outsole