Results are shown in Tab. I. Whereas adsorption data on Vycor does not show a significant change of pore geometry, in Gelsil samples surface area and pore volume were found to de- crease strongly due to silanation. The effect of silanation on the pore diameter is ≈ 0.2 nm, corresponding to a HDMS layer thickness of ≈ 0.1 nm. For comparison Kremer et al. [25] estimated the thickness of the silan layer from analysis of dielectric strength data as 0.38 nm. 

Filling with the fragile low molecular weight glass former [33] phenylsalicylate [salol, C$_{13}$H$_{10}$O$_{3}$, T$_{m}$(bulk)= 316 K] is done by capillary wetting at 333 K for 12h. Filling fractions f are evaluated via weighing clean and filled samples. 

Some characterizing parameters for the glass-freezing behavior of bulk salol are: fragility index m - which usually varies from m=17 for strong glass formers to m=150 for fragile ones - takes for salol [34] the value m=73, T$_{g}$(bulk)= 220 K (glass transition temperature defined at τ =100 s) and T$_{V F}$ =175 K [35] (Vogel-Fulcher temperature). The volume of a salol molecule is estimated [36] as 0.282 nm 3 corresponding to a mean diameter of about 0.8 nm. 

## B. Dynamic mechanical analysis 

The dynamic mechanical response of samples of a typical size of 1 x 2 x 8 mm 3 in three point bending (3PB) mode yields the real and imaginary part of the complex Young’s mo- dulus Y $^{∗}$= Y $^{′}$+ iY ′′ within a frequency range of 0.01 to 100 Hz applying static and dynamic forces up to 9.8 N. For further details see Refs. 23, 24, 37 and 38. Temperature is controlled by gaseous nitrogen flow from 120 K to RT. DMA analyzers are decoupled from building vibrations, and electronics are shielded from a possible interference with the 50 Hz mains voltage frequency. The analyzers used are a series 7 DMA and a Diamond DMA, both built by Perkin Elmer Inc. 

## C. Resonant ultrasound spectroscopy 

Due to contact errors a DMA experiment does not yield absolute values for elastic moduli. Therefore resonant ultrasound spectroscopy (RUS) was used to determine bulk and shear 

