Cfrgtkky

I would the sentence "out of column width" be inside the correspondent column.
Any suggestions? Ideally, this should be valid for a longer sentence (after reaching the established column width, the sentence skips to the next line).

begin{table}

    setlengthbelowcaptionskip{abovecaptionskip}

    setlengthabovecaptionskip{0pt}

    centering

    caption{tabular}



    begin{tabular}{*{6}{c} }

        toprule

        Reference         & Laminate      & Veil      & $bar{c}$  & $G$textsubscript{IC}  vs.{}    & $G$textsubscript{IIC} vs.{}  \

        &        &        &    & baseline     &  baseline \

        midrule

        mr{Kuwata cite{Kuwata2011, Kuwata2011a}} & Carbon/epoxy & mr{CoPA} & mr{0.39} & mr{} & mr{Out of column width} \

        &   Carbon/vynil ester     &        &        &        &   \

        Barjasteh cite{Barjasteh2017} & Carbon/benzoxazine & PA12 & 0.72 &  &    \ 

        Saz-Orozco cite{Saz-Orozco2015}    & Glass/vynil ester  & PA66 & 0.76 &  &  \ 

        O'Donovan cite{ODonovan2014}   & Glass/polyester & PA66 & 0.76 &  &   \ 

        Ram'irez cite{Ramirez2015}    & Carbon/epoxy & PEEK & 0.76 &  &   \ 

        Ni cite{Ni2015}    & Carbon/epoxy & Aramid & 0.94 &  &   \ 

        Nash cite{Nash2015a,Nash2016a} & Carbon/benzoxazine & PA & 1.65 &  &   \ 

        mr{Kuwata cite{Kuwata2011, Kuwata2011a}} & Carbon/epoxy & mr{CoPE} & mr{1.77} & mr{} & mr{} \

        &   Carbon/vynil ester     &        &        &        &   \

        Wong cite{Wong2017}    & Carbon/epoxy & Kevlar & 1.92 &  &   \ 

        Fitzmaurize cite{Fitzmaurice2016}  & Glass/polyester & PET & 2.03 &  &   \ 

        Saz-Orozco cite{Saz-Orozco2015}    & Glass/vynil ester & PET & 0.96 &  &   \ 

        mr{Beylergil cite{Beylergil2018}} & mr{Carbon/epoxy} & mr{PA66} & 0.96 & mr{} & mr{} \

        &       &        &    2.80    &        &   \

        mr{Ram'irez cite{Ramirez2015}} & mr{Carbon/epoxy} & mr{PPS} & 0.68 up to 3.43 &  & mr{} \

        &       &        &    0.49 up to 2.40   &        &   \  

        bottomrule

    end{tabular}

end{table}

Well, your given code snippet does not compile, because we do not know the definition of command mr and we do not have your used bib file nor the code you use to build the bibliography ...

With a little bit guessing I used the following code

documentclass{article}



usepackage{booktabs}

usepackage{showframe} % <==============================================

newcommand{mr}{} % <==================================================



begin{document}

begin{table} 

setlengthbelowcaptionskip{abovecaptionskip} 

setlengthabovecaptionskip{0pt} 

centering 

tiny % <===============================================================

caption{tabular}

begin{tabular}{*{5}{c}p{2cm}} % <======================================

    toprule

    Reference         & Laminate      & Veil      & $bar{c}$  & $G$textsubscript{IC}  vs.{}    & $G$textsubscript{IIC} vs.{}  \

    &        &        &    & baseline     &  baseline \

    midrule

    mr{Kuwata cite{Kuwata2011, Kuwata2011a}} & Carbon/epoxy & mr{CoPA} & mr{0.39} & mr{} & mr{Out of column width} \

    &   Carbon/vynil ester     &        &        &        &   \

    Barjasteh cite{Barjasteh2017} & Carbon/benzoxazine & PA12 & 0.72 &  &    \ 

    Saz-Orozco cite{Saz-Orozco2015}    & Glass/vynil ester  & PA66 & 0.76 &  &  \ 

    O'Donovan cite{ODonovan2014}   & Glass/polyester & PA66 & 0.76 &  &   \ 

    Ram'irez cite{Ramirez2015}    & Carbon/epoxy & PEEK & 0.76 &  &   \ 

    Ni cite{Ni2015}    & Carbon/epoxy & Aramid & 0.94 &  &   \ 

    Nash cite{Nash2015a,Nash2016a} & Carbon/benzoxazine & PA & 1.65 &  &   \ 

    mr{Kuwata cite{Kuwata2011, Kuwata2011a}} & Carbon/epoxy & mr{CoPE} & mr{1.77} & mr{} & mr{} \

    &   Carbon/vynil ester     &        &        &        &   \

    Wong cite{Wong2017}    & Carbon/epoxy & Kevlar & 1.92 &  &   \ 

    Fitzmaurize cite{Fitzmaurice2016}  & Glass/polyester & PET & 2.03 &  &   \ 

    Saz-Orozco cite{Saz-Orozco2015}    & Glass/vynil ester & PET & 0.96 &  &   \ 

    mr{Beylergil cite{Beylergil2018}} & mr{Carbon/epoxy} & mr{PA66} & 0.96 & mr{} & mr{} \

    &       &        &    2.80    &        &   \

    mr{Ram'irez cite{Ramirez2015}} & mr{Carbon/epoxy} & mr{PPS} & 0.68 up to 3.43 &  & mr{} \

    &       &        &    0.49 up to 2.40   &        &   \  

    bottomrule

end{tabular}



end{table}

end{document}

resulting in

Please see that I used tiny to get a smaller font and used p{2cm} to get a line breaking in the column if needed after 2cm ...

Package showframe is used to visualize the typing area and margins ...