paperboard contains crosslinked fibers the paperboard of the present application can be made in a single ply a two ply construction or a multi ply construction as desired while the paperboard of the present application may employ synthetic fibers as set forth above it is most preferred that paperboard comprise all or substantially all of the cellulosic fibers the distinguishing characteristic of the present application is that at least one ply of the paperboard whether a single ply or a multiple ply structure contains crosslinked cellulosic fibers the crosslinked cellulosic fibers increase the bulk density of the paperboard and thus the insulating characteristics as used herein crosslinked cellulosic fibers are kinked twisted curly cellulosic fibers it is preferred however that the fibers be produced by intrafiber crosslinking of the cellulosic fibers as described earlier paperboard of the present application may have a broad set of characteristics for example its basis weight can range from 200 gsm to 500 gsm more preferably from 250 gsm to 400 gsm most preferably the basis weight of the paperboard is equal to or greater than 250 gsm to achieve the insulating characteristics of the present invention it is preferred that the paperboard has a density of less than 0 5 g cc more preferably from 0 3 g cc to 0 45 g cc and most preferably from 0 35 g cc to 0 40 g cc when at least one ply of the paperboard contains crosslinked cellulosic fibers in accordance with the present invention advantageous temperature drop characteristics can be achieved these temperature drop characteristics can be achieved by altering the amount of crosslinked cellulosic fiber introduced into the paperboard by adjusting.