Many scientific investigations have been performed regarding Santa Claus , but never before has a rheological analysis of St. Nick been undertaken. Let me change that.
The need for Santa to exhibit non-Newtonian rheology is obvious on several fronts. All chimneys by design have a narrower opening at the top than at the bottom and in cases of interest, the opening at the top of the chimney is smaller than Father Frost himself. In order to transverse such geometric disparities, it is necessary that Santa's body be of a soft, gel-like material (more on this below), that can be greatly deformed without mechanical failure. While it may be further desired that full elastic recovery is achieved, it appears that this is in fact beyond the capabilities of Kris Kringle. For support of this conclusion, examine the three representative illustrations below of Pere Noel. They are similar, indicating a goodly amount of elastic recovery has been obtained, but the differences clearly indicate that full recovery was not recovered and furthermore that viscous flow has occurred.
Rheological understanding is also needed to clarify the events occurring while Babbo Natale is flowing through the chimney. Going up and down the chimney leads to conditions of both shear and, depending on the flow direction, either extensional or expansive flow. It is desired that the Jolly Old Elf be able to flow freely in order to rapidly accomplish his worldwide sojourn. As a rheopectic St. Nick would be highly undesirable in achieving this (his rate of flow would decrease the faster that he tried to move), we can conclude that Sinter Klaas's viscosity decreases both in shear and extension, strongly indicative of pseudoplasticity. (The discussion here has focused on steady-state dynamics; flow under transient conditions (start-up and cessation of flow) are left as an exercise for the interested student.)
In summary, I have unequivocally demonstrated that Santa Claus 1) is made of a non-Newtonian gel that shows both viscous and elastic behavior, and 2) exhibits pseudoplastic flow characteristics.
Before concluding, the author is compelled to state his shock that the rheology of Santa Claus has never been discussed to any serious extent, let alone this thoroughly. The link between Santa and rheology was first noticed 190 years ago, back in 1823(!) when the eminent American rheologist Clement Moore  published his famous poem, "A Visit from Saint Nicholas", perhaps better know as "Twas The Night Before Christmas". In that, he described Saint Nicholas as having "...a little round belly, That shook when he laugh'd, like a bowl full of jelly". Jelly! Probably the oldest known gel of all and a classic material with intriguing rheological characteristics. How many times has that line been read and heard and spoken, and yet never once has the connection been made to the larger aspects of Santa's rheological nature!? For shame. There are many professional rheologists this year that are going to be receiving a lump of coal in their stockings and it won't be high grade anthracite, but a well-deserved stinky, sulfur-laden lump of lignite instead.
 These certainly could be called pseudo-scientific or tongue-in-cheek-scientific as well, such as this perspective from North Carolina State. Or what you are reading here today.
 Ok, so he was just some guy that noticed a little rheological behavior and now he's going to cash in big on it. It's no different than what happened with Deborah Deborah or Heraclitus.